Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
The spatial distribution of global tropical sea surface temperature (SST) anomalies has not changed significantly since our last posting on September 26th. Positive anomalies persist (keep in mind the seasonal cycle) across the central Indian Ocean and from the date line to the west coast of South America, with weekly mean values ~plus .5-1.0C (around plus 2C west of South America). Above average SSTs also remain from the Caribbean into much of the Tropical North Atlantic Ocean. Below normal SSTs are still present from about 90-150E within 25-30 degrees of the equator. Actual SSTs of 29C and greater continue over the central Indian Ocean, from east of the Philippines to the South Pacific centered ~160E and on “both sides” of Central America. A recent development since the last posting has been a decided cooling (~minus .5-1.0C) of equatorial SSTs from around the date line to near the west coast of South America, as well as portions of the Tropical Northwest Pacific.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and
remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Since about September 1st, tropical convective forcing has been coherently propagating eastward west of the date line, generally along and north of the equator. This forcing “originated” around Africa, and while undergoing some complex variations, its propagation speed has remained around 4-5 m/s (3-4 deg long/day). Monitoring tools such as the Wheeler phase diagram and coherent modes Hovmollers indicate this region of enhanced tropical rainfall projects onto a Madden-Julian Oscillation (MJO), and I agree. In fact, I would consider it at least a moderate MJO for this time of year.
On about September 28th this MJO consolidated with a Rossby mode over the warm SSTs near 10-15N/155E, leading to an intense convective flare-up with negative OLR anomalies of at least minus 90W/m**2. Centered near 155E, there was an upstream (downstream) westerly wind burst (trade wind surge) on the equator with wind speed anomalies of at least 5m/s (leading to anomalous convergence). The anomalous westerlies did shift off the equator into both hemispheres, and “led” to some enhancement along the SPCZ as well. A reinvigoration of both convection and anomalous surface westerlies occurred near the equatorial date line a couple of days ago.
Current full disk satellite imagery shows the tropical convective forcing with the MJO extending from equatorial date line to near 15N/140E. There is also other enhancement across the North Tropical East Pacific ITCZ due to at least one convectively coupled Kelvin wave emanating from the MJO, as well as a flare-up around the Bay of Bengal. Strong suppression exists from far east Africa into the most of the Indian Ocean.
Anomalous upper tropospheric westerlies across the Western Hemisphere have been one of the responses to the MJO. Per animations of daily mean 150mb vector wind anomalies, there have been at least 2 “wavy” bands, with one across the equatorial atmosphere (moving into Africa) and the other extending from ~10N/180 into the western portion of the USA (leading to the current heavy precipitation across portions of the Southwest). Anomalies have been ~15-25m/s. Per time-latitude section of 200mb zonal mean zonal wind anomalies, westerly anomalies ~5m/s have been present since about September 30th from 0-30N (with other zonal mean interhemispheric symmetry of anomalies).
As would be expected, based on the reanalysis data (and its 1968-1997 climatology), the tendency of global relative AAM is strongly positive with a magnitude of ~25 Hadleys. Much of that contribution (in the zonal mean) started just north of the equator about a week ago, and is currently shifting poleward. Both the global mountain and frictional torques remain positive (latter recently increasing due to the trades). The global AAM based on both the reanalysis and operational data sets is near average (but obviously increasing). The interested reader needs to look at the actual plots (from the ESRL/PSD web site) to grasp the important details of the distribution of zonal mean AAM anomalies as well as the torques and transports.
To summarize, I think we have 1) a weak warm event whose future evolution is unclear (perhaps in doubt), 2) at least a moderate MJO signal, 3) at least one convectively coupled Kelvin wave moving into the East Pacific as I type (which could “speed things up a lot”), 4) tropical convective forcing from the Indian Ocean Dipole, which is another SST boundary forced component that could become important once again, 5) a sub-monthly component involving the global mountain torque, 6) a baroclinic wave packet interacting with the west central/northwest Pacific tropical forcing (with distorted twin subtropical anticyclones) which is part of the GSDM Stage 2 process (not discussed) and 7) the usual lots and lots of white noise.
There are two points I want make having given the above very brief background on the current weather-climate situation. First, the anomalously cool SSTs around Indonesia have been expanding eastward for about the past week-10 days while the SSTA tendency has been negative along the equatorial cold tongue. There has also been cooling across the Tropical Northwest Pacific particularly around the Philippines. This needs to be monitored! There are numerous scenarios that can be envisioned including the reflection of our recent oceanic Kelvin wave back to the west as an upwelling oceanic Rossby mode. This all means the future evolution of our current warm El-Nino is unclear, including the possibility it could weaken or even dissipate during the next few months.
The second point is I think we are transitioning into GSDM Stage 2 given the MJO and earth –atmosphere angular momentum budget situation. Most numerical models and their ensembles have generally captured this change. How long GSDM Stage 2 will persist is unclear. My thoughts for the MJO is that the dynamical signal will continue its movement into the Western Hemisphere (as currently shown by Hovmoller plots of 200mb velocity potential), increasing to around 10 deg long/day. The Western Hemisphere ITCZs are likely to become enhanced (including perhaps the SACZ). Tropical convection may persist around the date line and increase across Africa into the Indian Ocean. Thus a transition to GSDM Stage 3 and even Stage 4 may occur during weeks 2-3. My predictability confidence is about average for week 1 (everything considered!), then very low for weeks 2-3.
Week 1 (07 – 13 October 2006): GSDM Stage 2 is most probable. This will manifest itself as a large amplitude mid/upper tropospheric ridge along the west coast of North America into Alaska/western Canada and an anomalously deep trough around the Mississippi Valley. In fact, the NCEP GFS ensemble predicts ~minus 3 sigma 500mb height anomalies at tau 168hrs from 0000 UTC 6 October 2006 initial conditions. Thus below to well below normal temperatures are probable from the east slopes of the Rockies into much of the central and eastern parts of the country while the Pacific Northwest has very warm temperatures. In fact, widespread record low temperatures (at least) may occur across much of the north/central Plains into the Great Lakes states after areas such as the Front Range into the Great Lakes see their first “flakes of snow”.
Above average precipitation is probable generally east of the Mississippi River while the western third of the country is dry (after this weekend). Depending on the magnitude of the baroclinic development roughly the middle of next week, high winds are possible across much of the north central states along with a possibility of severe local storms along the cold front centered on the Ohio and Tennessee Valleys.
The Tropical North Atlantic looks to remain suppressed for tropical cyclone activity while the Central and East Pacific becomes more active. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (14 – 20 October 2006): The circulation may transition to GSDM Stage 3. For this time of year, we may see a relatively strong North Pacific Jet lead to a split flow pattern across much of North America (not the strong jet that may be seen during January, for example, during a warm event). This flow pattern will probably include a subtropical jet. Much of the lower 48 states should experience near-above normal temperatures, meaning a warming trend for the central and east (“Indian Summer”). Most of the country would also be dry. The East Pacific (along with the West and perhaps Central Pacific) may become (remain?) quite active with tropical cyclone activity, possibly spreading into the Southwest Caribbean (sooner?).
There is only one problem I have with the above. I have concern that the cool SSTs across the Tropical Northwest Pacific could lead to some persistence of the GSDM Stage 2 regime which evolves during week 1 (perhaps even retrograde it). There are a few numerical and statistical tools which imply this (without having much clue of the tropical convective forcing during week 2; it is coming from initial condition information).
Week 3 (21 – 27 October 2006): Unclear.
Overall, I do not see a wet period for Southwest Kansas through at least week 2. Some light precipitation is probable around Sunday Night into Monday and perhaps around the middle of next week. Cooler than normal temperatures look like a good bet during week 1, especially starting Monday. Temperatures may moderate to about normal week 2 (understanding daily variability). Monitoring will be needed to get a better sense for week 2 and beyond. For instance, if a 20-30 degree retrogression of the week 1 positive PNA pattern were to occur with a subtropical jet entering the Desert Southwest, a different outcome to the weather experienced than implied above is likely.
I will try to do an update to this blog next week. Please see the Appendix.
Appendix
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Ed Berry
Friday, October 06, 2006
Monday, September 25, 2006
Convection Creeping East - 25 September 2006 (to be, or not to be, an MJO)
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings. The following is a guest contribution from Klaus Weickmann of ESRL/PSD. I added some additional input such as the week 1-3 outlooks and the “parenthetical title above”.
Sea surface temperatures anomalies over the Indo-Pacific continue to resemble the mature stage of an El Nino. The total SSTs also reflect the phase of the seasonal cycle with 29C water extending from northeast of the Philippines and then southeast to a broad region around the date line. Another large band of anomalously warm water extends from the Gulf of Mexico southeast toward the tropical Atlantic. Smaller areas are present to the west of Central America and in the West Indian Ocean.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Since early August 2006, equatorial convection has been more or less enhanced over the western Indian Ocean near 60E, suppressed along 80-100E and enhanced over the western equatorial Pacific. This pattern is producing the “spread out” convective regime typical of El Nino events. Kelvin and Rossby wave activity has contributed to transient fluctuations of the convective pattern with the most recent intensifications occurring over the Indian Ocean in the first 10 days of September and the west Pacific (120-140E) in the most recent seven days. Thus since our last update more than a week ago, the center of tropical convective forcing has moved east and now extends in a broad band from the Arabian Sea to near the equator at 160E where it splits into two bands, one southeast along the SPCZ and the other northeast along the ITCZ. There is a projection onto a MJO, with the Wheeler index (greater than 1 sigma) suggesting a convective center north of Indonesia.
Current full-disk satellite imagery has the centroid of the forcing ~10N/140E, and rough calculation gives an eastward movement of 6m/s (~ 4-5 degrees of longitude/day) during the last 17 days. The daily mean surface vector wind anomalies from September 24th indicated equatorial westerly wind anomalies of ~5-10m/s accompanying this tropical forcing. The latest 5-day averaged TAO buoy array data also supports the presence of these surface westerlies, and may be a westerly wind event accompanying possibly a moderate MJO. This evolution needs to be CAREFULLY monitored particularly for impacts onto our warm event (understanding seasonal cycle issues).
Upper level easterly wind anomalies cover most of the equatorial region to the west of Indonesia and continue west toward South America. Westerly flow anomalies have developed from east of the date line to South America. Between these two bands of equatorial wind anomalies, cross equatorial flow over the western Pacific appears as the root of the strong subtropical jet that extends across the subtropical Pacific and feeds into the trough over the eastern USA. The trough is the result of an anticyclonic wave break over the northeast Pacific that can be linked to the convection over the west Pacific via a deep trough near the date line about 4 days ago (~20 September).
Despite these tropical connections, the mid-latitude wave pattern has been mostly progressive over the Pacific Ocean for the last 10-15 days and over the next few days baroclinic wave activity (including the remnants of Super Typhoon Yagi) is expected to amplify a ridge along the USA west coast and produce a deep trough over the east USA by the middle of this week. The models are all consistent with this development and maintain the trough for several days. Tropical convection should stay active over the western Indian Ocean and the west Pacific with some eastward movement possible.
Several tropical cyclones have developed in the broad convective band across the eastern hemisphere and activity should continue to be favored there, especially over the western Pacific. Currently a Kelvin wave is moving east and exciting convection along the ITCZ east of the dateline so this area also needs to be watched. Over the North Atlantic Ocean the easterly upper level wind anomalies are contributing to a low shear environment but subsidence is strengthening in the region. If convection over the western Pacific moves farther east the shear environment may become less favorable for tropical cyclone development over the eastern tropical Atlantic. The progressive wave pattern in mid-latitudes combined with stronger than normal westerly flow aloft over the southern USA has helped steer tropical cyclones away from the US mainland.
To summarize, I think we have 1) a weak warm event whose future evolution is still unclear, 2) a strengthening MJO signal, 3) at least one convectively coupled Kelvin wave moving into the Western Hemisphere as I type (which could “speed things up a lot”), 4) tropical convective forcing from the Indian Ocean Dipole (enhancement (suppression) to the west (east)), which is another SST boundary forced component, 5) a sub-monthly component that has contributed to mixed global AAM signals especially from the East Asian Mountain torque, and 6) lots and lots of white noise. Of course, the global circulation is well on its way to boreal autumn, only adding more uncertainty.
So, where is the global circulation within the GSDM framework? Global AAM signals are relatively weak and mixed. There are still zonal mean easterly wind anomalies throughout much of the subtropical atmosphere contributing to tropospheric AAM anomalies of at least minus ½ sigma based on the reanalysis data through 9/22 (zonal mean easterly anomalies roughly 2-5m/s at 200mb). However, there are robust regional and zonal mean signals (especially from the Southern Hemisphere) including a recent positive AAM tendency just north of the equator, consistent with the development of the upper tropospheric westerly wind anomalies discussed above. I think we are in a GSDM Stage 2 situation, and GSDM Stage 3 (warm El-Nino response) may be probable for weeks 2-3 particularly if the MJO signal remains in tact. Uncertainty remains very high for any predictions.
Week 1 (27 September – 02 October 2006): GSDM Stage 2 transitioning to Stage 3 is the best I can offer. Much of this period will be characterized by a ridge along the USA West Coast with an anomalously deep trough just east of the Mississippi River. This means essentially warm/dry for the western states, cool with light precipitation possible for the North Central States then wet from mainly the Mid-Atlantic-New England. There may also be a period or two of rainfall across the Deep South linked to jet streaks along the along the subtropical jet. Record low temperatures for this time of year are probable particularly for locations around the Great Lakes while portions of the West may experience record highs. This regime may deamplify toward the end of this period.
The Tropical North Atlantic looks to remain suppressed for tropical cyclone activity while the East Pacific becomes more active. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (03 – 09 October 2006): GSDM Stage 3 may be most probable. For this time of year, we may see a relatively strong North Pacific Jet lead to a split flow pattern across much of North America (not the strong North Pacific Jet that may be seen during January, for example, during a warm event). This flow pattern will probably include a subtropical jet. Much of the lower 48 states should experience near-above normal temperatures. One or two respectable mobile synoptic-scale troughs may move from west-east spreading precipitation with them. Moisture return from the Gulf of Mexico will be an issue for the central part of the country, especially for concerns about severe local storms. The East Pacific (along with the West and perhaps Central Pacific) may become quite active with tropical cyclone activity, possibly spreading into the Southwest Caribbean.
Week 3 (10 – 16 October 2006): Unclear. We may see an evolution to GSDM Stage 4 should a decent dynamical signal projecting onto an MJO move into the Western Hemisphere.
Week 1 does not look wet for Southwest Kansas, which is no surprise given climatology. With possible daily variations, temperatures should average to around normal. Week 2 seems probable to warm to above average with maybe better chances for rain later during the period. If GSDM Stage 4 appears during week 3, rain chances may improve at that time.
It is unlikely for me (Ed Berry) to do regular postings for at least the next 2 weeks, but please keep checking. Hopefully during week 3 I can start to maintain at least one posting/week, especially given the current weather-climate situation.
Appendix
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Klaus Weickmann and Ed Berry
Tuesday, September 19, 2006
Truce
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
Global tropical SSTs remain above average across the Western Hemisphere particularly along the equatorial Pacific cold tongue. Weekly mean anomalies (September 10-16) were ~plus 1-2C with values ~plus 3C west of South America. At depths of roughly 100m magnitudes ~plus 3-4C were present around 130W along the equator per latest TAO buoy data (September 18th). The latter are the result of weak eastward propagating oceanic Kelvin waves initiated by past westerly wind events on the equator across the west central Pacific. Again, the seasonal cycle of SSTs needs to be kept in mind with these anomalies. Climatologically SSTs along the equatorial cold tongue are cooling this time of year. Actual cold tongue SSTs vary from around 22C near the South American coast to in excess of 30C just west of the equatorial date line with the 29C isotherm at about 165W. Recall we use the 29C SST as a threshold for supporting persistent deep moist tropical convection.
SSTs across the equatorial Indian Ocean have cooled as a response to recent clouds and rainfall in that region, while substantial negative anomalies (~ minus 1-2C) remain around Indonesia south of the equator. Finally, respectable positive anomalies of SSTs also extend from the date line to the coast of Southeast Asia, with large “pools” of 29C and greater values. As I have stated in earlier postings, cool Indonesian SSTs with warm SSTs around the date line and east are typical of warm ENSOs in their mature phase which usually occurs during boreal winter. Literally only time will tell us how our current weak warm event evolves (models understood). I personally feel this is unclear (see past postings), also understanding equatorial Pacific SST anomalies this time of year tend to persist through winter. Please see the appropriate web sites for global SST details.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
The MJO signal is once again very weak, assuming we actually did have one a week to 10 days ago. This matter brings up an important related point. In general, with out getting into the level of detail I would use to scientifically defend this issue, the MJO signal has been generally weak since about 2002. I have raised this point in past writings, and may be related to a longer term global change signal such as global warming. However, the point is even when there are strong MJOs, on average these convectively coupled modes on explain ~20% of the tropical convective forcing. Additionally, no two MJOs are the same. If anyone is going to attempt to use MJO information for predictive purposes, detailed disciplined daily monitoring within a dynamical framework is required (understanding the importance of averaging to extract low frequency signals)! This is one of the motivations for deriving the GSDM. Rules of thumb based on statistical techniques, indices, etc., have their usefulness; however, there is no cookbook (insert picture of angry dog showing fangs)!!!
Taking the above one step further, we have been dealing with a weather-climate situation where signals have been weak since at least April 2006 (2002?). This does include tropical convective forcing arising from highly complicated nonlinear dynamical interactions with the extratropics (with forcing and responses then switching and “going all over the place” like any white noise process would) which project onto anything but MJOs. Again, only disciplined detailed daily monitoring within a dynamical framework linking weather and climate and research support (to help with numerical modeling work) has any hope of catching these things, particularly for efforts such as improving predictions of extreme weather events for days 3-14. And please remember, such kind of information must be expressed probabilistically for needed periods of time, and that numerical models do very poorly predicting tropical convective flare-ups after about day 5.
During the last 3-5 days a consolidation of tropical convective forcing has occurred centered around 10-15N/120E. Full-disk satellite imagery shows a nice band of enhanced tropical convection extending from the northern Arabian Sea east-southeast across northern Indonesia (keep in mind the SSTs) into the South Pacific islands. Frontal activity from the Southern Hemisphere is contributing to the extension into the SPCZ (which is by definition). Per coherent modes Hovmollers an eastward propagating convectively coupled Kelvin wave from the Indian Ocean merging with a Rossby mode from the west Pacific may have contributed to the merger. Three-day averaged OLR anomalies are ~minus 50-70 W/m**2. The anomalous convection that was across the equatorial Indian Ocean roughly 2 weeks ago has shifted to about 20N leaving suppression in its wake (as expected from the seasonal cycle), leading to the band of thunderstorm clusters (see links for possible regions of tropical cyclogenesis). Weaker tropical forcing remains across the northern equatorial date line region, and from the Americas into the North Atlantic and Africa.
My own thoughts, with very low confidence, are there will be a fairly rapid eastward propagating convectively coupled mode (dynamical signal) from the location of the consolidation into the Tropical Northwest Pacific and date line regions. Frontal activity from the Southern Hemisphere may also excite tropical thunderstorm activity across the warm SSTs around the date line. Thus by late week 1 into week 2 we may observe positive anomalies of tropical convection from around the date line into the Philippines and perhaps Southeast Asia. Other areas of tropical forcing may remain around the Americas and North Atlantic, and perhaps re-emerge across the Indian Ocean just south of the equator (where SSTs are still slightly above average). In fact, frontal activity from the Southern Hemisphere may already be starting the latter. The forcing across the Western Hemisphere may be a local response linked to the Indian Ocean flare-up 2 weeks ago and perhaps even our weak warm ENSO.
Based on monitoring during the past several months (and boreal falls from several past years) I would not be surprised to see two regions of tropical convective forcing across both the equatorial Indian Ocean and west central Pacific re-appear during the next 1-3 weeks. My defense for that notion is still the loose presence of these 20-30 day modes of tropical convective variability which may (and not defensible at this time) be linked to submonthly modes in the extratropics.
Global AAM signals are still not clear. Global mountain torque, based on the reanalysis data through September 16th and its 1968-1997 climatology, is still at about plus 10 Hadleys with most of that coming from East Asia. The global frictional torque is roughly minus 10 Hadleys, with most of that coming from intense storm track activity across the Southern Hemisphere extratropics (probably also a contribution from the Coriolis torque). The former (along with the Earth component) is contributing to a positive global tendency of around 15 Hadleys while the latter has contributed to a global tropospheric relative AAM of about minus 1 sigma. I think I can see where a lot of this is coming from; however, it is not trivial for me to explain that without additional presentation resources. The following is a brief attempt.
If a time-latitude section of 200mb zonal mean zonal wind anomalies is done (care understood of just using one level), there is a signal of poleward propagation of zonal mean westerly wind anomalies (~ 5m/s) from the equator to presently around 30N and 30S starting early August 2006 linked to a central Pacific tropical convective flare-up. Given the seasonal cycle, these zonal mean westerlies may have re-invigorated what was already an active storm track season for the Southern Hemisphere extratropics. That may contribute a negative tendency to both the global frictional and Coriolis torques. Meanwhile, flare-ups across the warm SSTs of the west central Pacific may have contributed to (or be a response to) positive East Asian mountain torques. All of these behaviors may be warm ENSO signals, in the presence of other “things going on”.
Currently, there are 200mb zonal mean easterly wind anomalies throughout the tropical and subtropical atmospheres, with ~5m/s magnitudes. The more up to date ESRL/PSD operational global AAM plot (1979-1998 climatology) still has anomalies slightly less than minus 1 sigma, with strong signal of vertically averaged zonal mean Southern Hemisphere subtropical easterly winds (with some symmetry to the Northern Hemisphere). The 120E consolidation had led to the formation of twin subtropical anticyclones in that region, and these are linked to Rossby wave energy dispersions (RWDs) into both extratropics (per animations of 150mb and 250mb daily mean vector wind anomalies). These RWDs have recently contributed to strong anticyclones across the high latitudes of both hemispheres, and possibly an increase in the flux convergence of AAM transport at 30S and perhaps starting to appear at 30N on September 16th.
Turning to the Asia-Pacific-North American sector, not only is there anomalous outflow of upper tropospheric southwesterly flow from the 120E convection, there is another source starting near the date line (see plots and animations on the ESRL/PSD web site). The former is loosely from many modes of subseasonal variability while the latter is a warm ENSO signal (also contributing to short time scale processes). These outflows are contributing to subtropical jets (STJs). The outflow tied to the 120E consolidation linked up with a baroclinic wave packet moving through northern Asia a couple of days ago. It is this interaction which may lead to a second trough across the western USA by this weekend after its predecessor. Recalling the local Western Hemisphere response from above, there have also been weak twin subtropical anticyclones from the East Pacific into the Atlantic.
To summarize, I think we have 1) a weak warm event whose future evolution is unclear, 2) the consolidation of tropical convective forcing around 10-15N/120E which may lead to an eastward propagating dynamical signal, 3) other arguably random regions of tropical convective forcing including the Western Hemisphere, 4) a sub-monthly component that has contributed to mixed global AAM signals especially for the East Asian Mountain torque, and 5) lots and lots of white noise. Of course, the global circulation is well on its way to boreal autumn, only adding more uncertainty. I do think that an intermediate state between GSDM Stages 4 and 1 best describe the current weather-climate situation. Uncertainty remains very high for any predictions.
Week 1 (20-26 September 2006): GSDM Stage 1 is most probable, with STJ interaction. Like nearly all the models show, 1-2 strong mobile synoptic baroclinic troughs digging into the western part of the country then heading east is probable. The details are unclear, especially for the second trough. My own feeling has been to favor, with very low confidence, the models depicting a slower and deeper solution for this second Rocky Mountain trough, as was shown by models such as the ECMWF 4-5 days ago. We are in a base state that favors troughs to break anticyclonically into the western USA states (which is why there would be a NE-SW tilt; there are also AAM transport considerations not discussed). During this week, portions of the Northern and Central Rockies are likely to experience heavy snowfall while severe local storms are probable from the Plains into the south central and southeast USA.
While temperatures colder than normal may persist over the western states, much of the Deep South will keep summertime. The Tropical North Atlantic will need to be monitored for any additional cyclone formation. Right now conditions for tropical cyclogenesis there remain favorable (from a weather-climate linkage viewpoint). With troughs digging into the western USA, the East Coast and Gulf States may become more vulnerable with time, particularly from hybrid systems. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (27 September – 03 October 2006): A transition to GSDM Stage 2 may be most probable, meaning an eastward shift of the week 1 pattern across the USA. The trough position may be become established ~95-100W with the ridge just off the west coast into Alaska. Synoptic features would be expected to modulate this pattern. However, I could see this situation being transient, with perhaps GSDM Stage 3 by the end of this week or during week 3. This is time of year we see the North Pacific Jet “outrun” the tropical convective forcing.
Week 3 (04-10 October 2006): Unclear. However, similar to past boreal autumns, a GSDM Stage 4-1 may return at some point as our “war of the oceans” resumes. This may return us to a synoptic pattern similar to the one now present across the USA.
I think opportunities for rainfall will exist for Southwest Kansas later this week for system # 1 and hopefully system #2 for the Friday-Saturday time frame. Per above, I have been weakly favoring the model solutions showing a slower closed Rocky Mountain cyclone for the latter. I hope we do not have problems with the dry intrusion for the second storm. I think another trough will follow for later next week into week 2; however, its maximum amplitude may occur across the central portion of the country meaning another chance for rainfall followed by another surge of a chilly airmass. Afterwards, right now I would have to favor odds toward near-above average rainfall with overall near normal temperatures (with likely large variations) possibly through most of October. I think there will be more strong western USA troughs for at least the next several weeks.
I may not be able to do another posting for the next 2-3 weeks due to so many commitments. Please keep checking.
Ed Berry
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
Global tropical SSTs remain above average across the Western Hemisphere particularly along the equatorial Pacific cold tongue. Weekly mean anomalies (September 10-16) were ~plus 1-2C with values ~plus 3C west of South America. At depths of roughly 100m magnitudes ~plus 3-4C were present around 130W along the equator per latest TAO buoy data (September 18th). The latter are the result of weak eastward propagating oceanic Kelvin waves initiated by past westerly wind events on the equator across the west central Pacific. Again, the seasonal cycle of SSTs needs to be kept in mind with these anomalies. Climatologically SSTs along the equatorial cold tongue are cooling this time of year. Actual cold tongue SSTs vary from around 22C near the South American coast to in excess of 30C just west of the equatorial date line with the 29C isotherm at about 165W. Recall we use the 29C SST as a threshold for supporting persistent deep moist tropical convection.
SSTs across the equatorial Indian Ocean have cooled as a response to recent clouds and rainfall in that region, while substantial negative anomalies (~ minus 1-2C) remain around Indonesia south of the equator. Finally, respectable positive anomalies of SSTs also extend from the date line to the coast of Southeast Asia, with large “pools” of 29C and greater values. As I have stated in earlier postings, cool Indonesian SSTs with warm SSTs around the date line and east are typical of warm ENSOs in their mature phase which usually occurs during boreal winter. Literally only time will tell us how our current weak warm event evolves (models understood). I personally feel this is unclear (see past postings), also understanding equatorial Pacific SST anomalies this time of year tend to persist through winter. Please see the appropriate web sites for global SST details.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
The MJO signal is once again very weak, assuming we actually did have one a week to 10 days ago. This matter brings up an important related point. In general, with out getting into the level of detail I would use to scientifically defend this issue, the MJO signal has been generally weak since about 2002. I have raised this point in past writings, and may be related to a longer term global change signal such as global warming. However, the point is even when there are strong MJOs, on average these convectively coupled modes on explain ~20% of the tropical convective forcing. Additionally, no two MJOs are the same. If anyone is going to attempt to use MJO information for predictive purposes, detailed disciplined daily monitoring within a dynamical framework is required (understanding the importance of averaging to extract low frequency signals)! This is one of the motivations for deriving the GSDM. Rules of thumb based on statistical techniques, indices, etc., have their usefulness; however, there is no cookbook (insert picture of angry dog showing fangs)!!!
Taking the above one step further, we have been dealing with a weather-climate situation where signals have been weak since at least April 2006 (2002?). This does include tropical convective forcing arising from highly complicated nonlinear dynamical interactions with the extratropics (with forcing and responses then switching and “going all over the place” like any white noise process would) which project onto anything but MJOs. Again, only disciplined detailed daily monitoring within a dynamical framework linking weather and climate and research support (to help with numerical modeling work) has any hope of catching these things, particularly for efforts such as improving predictions of extreme weather events for days 3-14. And please remember, such kind of information must be expressed probabilistically for needed periods of time, and that numerical models do very poorly predicting tropical convective flare-ups after about day 5.
During the last 3-5 days a consolidation of tropical convective forcing has occurred centered around 10-15N/120E. Full-disk satellite imagery shows a nice band of enhanced tropical convection extending from the northern Arabian Sea east-southeast across northern Indonesia (keep in mind the SSTs) into the South Pacific islands. Frontal activity from the Southern Hemisphere is contributing to the extension into the SPCZ (which is by definition). Per coherent modes Hovmollers an eastward propagating convectively coupled Kelvin wave from the Indian Ocean merging with a Rossby mode from the west Pacific may have contributed to the merger. Three-day averaged OLR anomalies are ~minus 50-70 W/m**2. The anomalous convection that was across the equatorial Indian Ocean roughly 2 weeks ago has shifted to about 20N leaving suppression in its wake (as expected from the seasonal cycle), leading to the band of thunderstorm clusters (see links for possible regions of tropical cyclogenesis). Weaker tropical forcing remains across the northern equatorial date line region, and from the Americas into the North Atlantic and Africa.
My own thoughts, with very low confidence, are there will be a fairly rapid eastward propagating convectively coupled mode (dynamical signal) from the location of the consolidation into the Tropical Northwest Pacific and date line regions. Frontal activity from the Southern Hemisphere may also excite tropical thunderstorm activity across the warm SSTs around the date line. Thus by late week 1 into week 2 we may observe positive anomalies of tropical convection from around the date line into the Philippines and perhaps Southeast Asia. Other areas of tropical forcing may remain around the Americas and North Atlantic, and perhaps re-emerge across the Indian Ocean just south of the equator (where SSTs are still slightly above average). In fact, frontal activity from the Southern Hemisphere may already be starting the latter. The forcing across the Western Hemisphere may be a local response linked to the Indian Ocean flare-up 2 weeks ago and perhaps even our weak warm ENSO.
Based on monitoring during the past several months (and boreal falls from several past years) I would not be surprised to see two regions of tropical convective forcing across both the equatorial Indian Ocean and west central Pacific re-appear during the next 1-3 weeks. My defense for that notion is still the loose presence of these 20-30 day modes of tropical convective variability which may (and not defensible at this time) be linked to submonthly modes in the extratropics.
Global AAM signals are still not clear. Global mountain torque, based on the reanalysis data through September 16th and its 1968-1997 climatology, is still at about plus 10 Hadleys with most of that coming from East Asia. The global frictional torque is roughly minus 10 Hadleys, with most of that coming from intense storm track activity across the Southern Hemisphere extratropics (probably also a contribution from the Coriolis torque). The former (along with the Earth component) is contributing to a positive global tendency of around 15 Hadleys while the latter has contributed to a global tropospheric relative AAM of about minus 1 sigma. I think I can see where a lot of this is coming from; however, it is not trivial for me to explain that without additional presentation resources. The following is a brief attempt.
If a time-latitude section of 200mb zonal mean zonal wind anomalies is done (care understood of just using one level), there is a signal of poleward propagation of zonal mean westerly wind anomalies (~ 5m/s) from the equator to presently around 30N and 30S starting early August 2006 linked to a central Pacific tropical convective flare-up. Given the seasonal cycle, these zonal mean westerlies may have re-invigorated what was already an active storm track season for the Southern Hemisphere extratropics. That may contribute a negative tendency to both the global frictional and Coriolis torques. Meanwhile, flare-ups across the warm SSTs of the west central Pacific may have contributed to (or be a response to) positive East Asian mountain torques. All of these behaviors may be warm ENSO signals, in the presence of other “things going on”.
Currently, there are 200mb zonal mean easterly wind anomalies throughout the tropical and subtropical atmospheres, with ~5m/s magnitudes. The more up to date ESRL/PSD operational global AAM plot (1979-1998 climatology) still has anomalies slightly less than minus 1 sigma, with strong signal of vertically averaged zonal mean Southern Hemisphere subtropical easterly winds (with some symmetry to the Northern Hemisphere). The 120E consolidation had led to the formation of twin subtropical anticyclones in that region, and these are linked to Rossby wave energy dispersions (RWDs) into both extratropics (per animations of 150mb and 250mb daily mean vector wind anomalies). These RWDs have recently contributed to strong anticyclones across the high latitudes of both hemispheres, and possibly an increase in the flux convergence of AAM transport at 30S and perhaps starting to appear at 30N on September 16th.
Turning to the Asia-Pacific-North American sector, not only is there anomalous outflow of upper tropospheric southwesterly flow from the 120E convection, there is another source starting near the date line (see plots and animations on the ESRL/PSD web site). The former is loosely from many modes of subseasonal variability while the latter is a warm ENSO signal (also contributing to short time scale processes). These outflows are contributing to subtropical jets (STJs). The outflow tied to the 120E consolidation linked up with a baroclinic wave packet moving through northern Asia a couple of days ago. It is this interaction which may lead to a second trough across the western USA by this weekend after its predecessor. Recalling the local Western Hemisphere response from above, there have also been weak twin subtropical anticyclones from the East Pacific into the Atlantic.
To summarize, I think we have 1) a weak warm event whose future evolution is unclear, 2) the consolidation of tropical convective forcing around 10-15N/120E which may lead to an eastward propagating dynamical signal, 3) other arguably random regions of tropical convective forcing including the Western Hemisphere, 4) a sub-monthly component that has contributed to mixed global AAM signals especially for the East Asian Mountain torque, and 5) lots and lots of white noise. Of course, the global circulation is well on its way to boreal autumn, only adding more uncertainty. I do think that an intermediate state between GSDM Stages 4 and 1 best describe the current weather-climate situation. Uncertainty remains very high for any predictions.
Week 1 (20-26 September 2006): GSDM Stage 1 is most probable, with STJ interaction. Like nearly all the models show, 1-2 strong mobile synoptic baroclinic troughs digging into the western part of the country then heading east is probable. The details are unclear, especially for the second trough. My own feeling has been to favor, with very low confidence, the models depicting a slower and deeper solution for this second Rocky Mountain trough, as was shown by models such as the ECMWF 4-5 days ago. We are in a base state that favors troughs to break anticyclonically into the western USA states (which is why there would be a NE-SW tilt; there are also AAM transport considerations not discussed). During this week, portions of the Northern and Central Rockies are likely to experience heavy snowfall while severe local storms are probable from the Plains into the south central and southeast USA.
While temperatures colder than normal may persist over the western states, much of the Deep South will keep summertime. The Tropical North Atlantic will need to be monitored for any additional cyclone formation. Right now conditions for tropical cyclogenesis there remain favorable (from a weather-climate linkage viewpoint). With troughs digging into the western USA, the East Coast and Gulf States may become more vulnerable with time, particularly from hybrid systems. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (27 September – 03 October 2006): A transition to GSDM Stage 2 may be most probable, meaning an eastward shift of the week 1 pattern across the USA. The trough position may be become established ~95-100W with the ridge just off the west coast into Alaska. Synoptic features would be expected to modulate this pattern. However, I could see this situation being transient, with perhaps GSDM Stage 3 by the end of this week or during week 3. This is time of year we see the North Pacific Jet “outrun” the tropical convective forcing.
Week 3 (04-10 October 2006): Unclear. However, similar to past boreal autumns, a GSDM Stage 4-1 may return at some point as our “war of the oceans” resumes. This may return us to a synoptic pattern similar to the one now present across the USA.
I think opportunities for rainfall will exist for Southwest Kansas later this week for system # 1 and hopefully system #2 for the Friday-Saturday time frame. Per above, I have been weakly favoring the model solutions showing a slower closed Rocky Mountain cyclone for the latter. I hope we do not have problems with the dry intrusion for the second storm. I think another trough will follow for later next week into week 2; however, its maximum amplitude may occur across the central portion of the country meaning another chance for rainfall followed by another surge of a chilly airmass. Afterwards, right now I would have to favor odds toward near-above average rainfall with overall near normal temperatures (with likely large variations) possibly through most of October. I think there will be more strong western USA troughs for at least the next several weeks.
I may not be able to do another posting for the next 2-3 weeks due to so many commitments. Please keep checking.
Ed Berry
Saturday, September 16, 2006
War Update
This is a short update to the previous posting issued on September 13th, 2006.
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Tropical convective forcing continues centered around 10N/100E with a weaker region near 0/160E. As suggested by the coherent modes Hovmollers and observed on full disk satellite imagery, convectively coupled Kelvin and Rossby waves have been emanating from the Indian Ocean and date line convection, respectively. A weak consolidation of these features is possible within the next few days. However, as far as I am concerned, there remain two distinct regions of tropical forcing across the Eastern Hemisphere, with the Indian Ocean dominating. Monitoring tools such as the Wheeler phase space plot and 5-day averaged 200mb velocity potential suggest that the weak Indian Ocean MJO signal may be stalling.
Over the last several days the trades have been intensifying from the central Pacific Ocean to near Indonesia, with a separate region of above average easterlies across the central equatorial Indian Ocean ~60-90E. Anomalies have generally been from 2-5m/s. While global tropical SSTs have not changed much during the past week, I want to make the point that the anomalous warming around the equatorial date line has been slowed, at least for now. Positive anomalies of ~plus 1-1.5C remain. There has also been a reduction of positive SST anomalies along the equatorial Pacific cold tongue from ~120-160W, with magnitudes ~0.5C. However, subsurface anomalies at depths of ~100m are still ~plus 3-4C in this region. These depth anomalies represent greater than normal deepening of the oceanic thermocline along the cold tongue, and not actual SSTs. In other words, upwelling these positive depth anomalies to the surface via enhanced trades does not necessarily mean warming of the ocean surface.
Animations such as 150mb and 250mb daily mean vector wind anomalies show a relatively clean signal of twin Indian Ocean subtropical anticyclones with down stream twin subtropical cyclones across Indonesia. This is the expected baroclinic response to the anomalous divergent outflow from the enhanced convection in that region. These features have been nicely linking up with baroclinic extratropical wavetrains, including Rossby wave energy dispersions across the Pacific Rim leading to the large anomalous anticyclonic gyre around and north of Alaska (and the downstream western USA trough). The latter has had daily mean wind anomalies of around 30-40m/s at 250mb. There are also loose twin anticyclones over the central and east Pacific, linked to the date line forcing (representing the warm ENSO signal).
While global AAM signals remain somewhat mixed, I think I can see the possibility of a response signal emerging. As of September 13th the global mountain torque was roughly 20 Hadleys (leading to a slight positive AAM tendency), with most of that coming from East Asia. Within the GSDM framework attribution may be to both the submonthly component and the tropical convective forcing from the west central Pacific. However, for about the past week-10 days (reanalysis data) there is some evidence from the AAM transports that fluxing out of the northern midlatitudes centered ~40N has been occurring. Overall, global relative AAM remains about 1 sigma below normal per reanalysis data climatology (1968-1997). This has translated to a split flow across the Pacific-North American sector, with weakly mean (September 10-16) anomalous westerlies of roughly 25m/s (operational data climatology) across the North Pacific at about 45N.
The point is I think I can see how the 2 regions of Indian Ocean dominated tropical forcing (with subsequent feedbacks and forcing from the extratropics) are currently impacting the global circulation, giving loosely a GSDM Stage 1-2 behavior. The role of the seasonal cycle and other nonlinear dynamical processes that are not well understood will determine where the coupled earth-atmosphere-ocean system goes from here. Included is the evolution of our weak warm ENSO; for example, “how big it will get and how long it will last”. Right now I feel the latter is unclear. For weeks 1-3, I think variations in the GSDM Stage 1-2 response is the only statistically useful outlook I think I can offer. Please see previous posting for the weekly outlooks.
I will try to do another posting on about the middle of next week (roughly Tuesday-Wednesday 9/19-20).
Ed Berry
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Tropical convective forcing continues centered around 10N/100E with a weaker region near 0/160E. As suggested by the coherent modes Hovmollers and observed on full disk satellite imagery, convectively coupled Kelvin and Rossby waves have been emanating from the Indian Ocean and date line convection, respectively. A weak consolidation of these features is possible within the next few days. However, as far as I am concerned, there remain two distinct regions of tropical forcing across the Eastern Hemisphere, with the Indian Ocean dominating. Monitoring tools such as the Wheeler phase space plot and 5-day averaged 200mb velocity potential suggest that the weak Indian Ocean MJO signal may be stalling.
Over the last several days the trades have been intensifying from the central Pacific Ocean to near Indonesia, with a separate region of above average easterlies across the central equatorial Indian Ocean ~60-90E. Anomalies have generally been from 2-5m/s. While global tropical SSTs have not changed much during the past week, I want to make the point that the anomalous warming around the equatorial date line has been slowed, at least for now. Positive anomalies of ~plus 1-1.5C remain. There has also been a reduction of positive SST anomalies along the equatorial Pacific cold tongue from ~120-160W, with magnitudes ~0.5C. However, subsurface anomalies at depths of ~100m are still ~plus 3-4C in this region. These depth anomalies represent greater than normal deepening of the oceanic thermocline along the cold tongue, and not actual SSTs. In other words, upwelling these positive depth anomalies to the surface via enhanced trades does not necessarily mean warming of the ocean surface.
Animations such as 150mb and 250mb daily mean vector wind anomalies show a relatively clean signal of twin Indian Ocean subtropical anticyclones with down stream twin subtropical cyclones across Indonesia. This is the expected baroclinic response to the anomalous divergent outflow from the enhanced convection in that region. These features have been nicely linking up with baroclinic extratropical wavetrains, including Rossby wave energy dispersions across the Pacific Rim leading to the large anomalous anticyclonic gyre around and north of Alaska (and the downstream western USA trough). The latter has had daily mean wind anomalies of around 30-40m/s at 250mb. There are also loose twin anticyclones over the central and east Pacific, linked to the date line forcing (representing the warm ENSO signal).
While global AAM signals remain somewhat mixed, I think I can see the possibility of a response signal emerging. As of September 13th the global mountain torque was roughly 20 Hadleys (leading to a slight positive AAM tendency), with most of that coming from East Asia. Within the GSDM framework attribution may be to both the submonthly component and the tropical convective forcing from the west central Pacific. However, for about the past week-10 days (reanalysis data) there is some evidence from the AAM transports that fluxing out of the northern midlatitudes centered ~40N has been occurring. Overall, global relative AAM remains about 1 sigma below normal per reanalysis data climatology (1968-1997). This has translated to a split flow across the Pacific-North American sector, with weakly mean (September 10-16) anomalous westerlies of roughly 25m/s (operational data climatology) across the North Pacific at about 45N.
The point is I think I can see how the 2 regions of Indian Ocean dominated tropical forcing (with subsequent feedbacks and forcing from the extratropics) are currently impacting the global circulation, giving loosely a GSDM Stage 1-2 behavior. The role of the seasonal cycle and other nonlinear dynamical processes that are not well understood will determine where the coupled earth-atmosphere-ocean system goes from here. Included is the evolution of our weak warm ENSO; for example, “how big it will get and how long it will last”. Right now I feel the latter is unclear. For weeks 1-3, I think variations in the GSDM Stage 1-2 response is the only statistically useful outlook I think I can offer. Please see previous posting for the weekly outlooks.
I will try to do another posting on about the middle of next week (roughly Tuesday-Wednesday 9/19-20).
Ed Berry
Wednesday, September 13, 2006
War of the Oceans!!!
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
Global tropical SSTs remain quite warm across the Western Hemisphere and the western/central Indian Ocean, with the greatest positive anomalies around the equatorial date line and the Eastern Pacific cold tongue. Magnitudes in the latter areas were at least plus 2C. In addition, the entire equatorial basin from ~160E to the west coast of South America has observed weekly mean (September 3-9, 2006) positive SST anomalies of ~1-2C. The latest 5-day averaged TAO buoy array data indicates anomalies up to plus 4C around 140W on the equator at 100m depth, with plus 1-2C anomalies common at depths of 100m east of the date line.
Anomalies of roughly plus .5-1.5C were still present across the Atlantic and much of the Indian Ocean. Below normal SSTs ~minus 1-2C continue around Indonesia, particularly south of the equator to the west coast of Australia. A thought is that the combination of cross-equatorial southerly flow linked to Southern Hemisphere cold outbreaks and upwelling has led to these cool anomalies. Hence we see a pattern of generally a “warm Indian Ocean-cool Indonesian region-warm date line region” in regard to SSTAs, typical of a mature warm ENSO event.
During much of the boreal summer, westerly wind anomalies and even actual westerlies have been common particularly along the equatorial date line region, leading to a deepening of the oceanic thermocline along the equatorial cold tongue (discussed above). However, during the last 5-10 days these westerly anomalies have weakened considerably with even weak easterly anomalies. More said about this below.
Actual SSTs in excess of 29C (threshold we use to maintain significant tropical convective forcing) remain present across portions of the Indian Ocean, and especially the equatorial date line and regions of the Caribbean. These SSTs are most extensive from ~150E-180 within 10 degrees of the equator (see links for further details).
Per the latest ENSO diagnostic discussion dated September 13th, 2006, “El Niño conditions have developed and are likely to continue into early 2007” (please see link below). I would agree with that, and only confirms some of the scientific issues discussed in past writings on this Blog. I sincerely applaud CPC for being proactive to get this information out to everyone!!
Nevertheless, I hope to make the point that the magnitude (and duration) of this event as we go into boreal winter, including global impacts, are unclear (understanding other signals such as trends and what statistics offer). There has been a lot of complicated random (stochastic) forcing going on in the coupled atmosphere-ocean system since at least April 2006. Some of these behaviors have been detailed in our latest weather-climate discussion (link above), and are outstanding research issues (let alone using these kind of notions to make predictions). Right now, only careful weather-climate monitoring within the GSDM framework offers any “hope” of catching these kind of complicated highly non-linear dynamical behaviors in real-time.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
From monitoring, I do feel that the events leading to the onset of weak warm event conditions across the equatorial Pacific Ocean has had at least “episodic impacts” to the global weather during boreal summer. These include general suppression (thus far) of the Tropical North Atlantic tropical cyclone season (understanding climatology and the situation right now), the increase of Tropical Northwest Pacific tropical cyclones (ex., southeast China), the excessive heat much of the USA has dealt with, and the recent change to a cooler and wetter weather pattern for many locations across the Great Plains. The important point to make is there are always forcing-response-feedbacks going on within the Earth-atmosphere-ocean system, and care needs to be offered to thinking that, “some kind of an event is too weak to have an impact”. While there is some truth to these kind of statements statistically (on average), from a weather-climate linkage point of view these notions can lead to difficulty when trying to capture the possibility of extreme weather events. Even on a case by case basis, statistically useful information can be offered for the latter when use of the appropriate framework is employed.
In contrast to the past few months (at least), there are actually at least a couple of weather-climate linkage signals to discuss. The flare-up across the equatorial Indian Ocean (linked to Rossby wave energy dispersions from the North Atlantic) discussed early last week has evolved into a convectively coupled mode at least weakly projecting onto a Madden-Julian Oscillation (MJO). Latest weakly mean OLR anomalies centered ~5-10N/70E were around minus 50-70W/m**2, and a rough calculation gives a phase speed for eastward movement of 5m/s (~4 deg long/day) for this feature (there is also a component moving northeast through India and the Bay of Bengal). The Wheeler phase space plot also lends some support to an MJO. The coherent modes modes Hovmollers show a very weak MJO projection, and also a Kelvin wave emanating to the east. Latest satellite imagery suggests the core of this tropical convective forcing centered ~5-10N/95E, with a Kelvin wave signature moving east along the equator.
There is also a second, less concentrated and weaker area of tropical convective forcing centered along and just north of the date line being forced by the very warm SSTs (discussed above) and other processes. A third (and even weaker) region exists across the Tropical Northeast Pacific. Loosely (for brevity) these last two regions represent an ENSO signal. The forcing across the Tropical North Atlantic and Africa is not well organized.
Now we come to the punch line of this posting that I hope to make clear. We have the convectively coupled dynamical forcing signal over the Indian Ocean and the SST boundary forcing around the date line of the central Pacific Ocean. That is, two areas of tropical forcing, and has been a behavior generally observed since early 2002 (global warming signal?). Which area (ocean) is going to dominate as we go into boreal winter? Obviously there are seasonal cycle considerations and perhaps that may be all we are seeing. Recall that the SSTs are warm across both regions of forcing, with the date line being the warmest where there has been less cloud cover and rainfall recently. Some brief thoughts follow.
Per animations of 150mb and 250mb daily mean vector wind anomalies along with additional tools such as Hovmollers of 250mb meridional wind anomalies, anomalous circulation features have reversed across the subtropical Eastern Hemisphere during the last week. There are now twin anomalous (~10-20m/s, at least) upper tropospheric subtropical anticyclones across the western Indian Ocean and downstream twin cyclones across Indonesia (forced by the divergent outflow) with gyres of the opposite sense in the lower troposphere (leading to some resumption of surface easterly wind anomalies at the date line). This is the expected baroclinic response from a convectively coupled mode such as a MJO.
Impacts onto the extratropics of both hemispheres from the Indian Ocean forcing are currently quite robust. As I type an intense Rossby wave energy dispersion is arcing from this tropical forcing across the North Pacific rim leading to the western USA trough that the numerical models are predicting for the next several days.
Impacts from the date line tropical convection are less robust. Twin subtropical anticyclones continue to appear “off and on”, and have contributed to the subtropical jet (STJ) currently extending into the Desert Southwest. The point is the Indian Ocean tropical forcing is currently dominating the global tropical/subtropical circulation (loosely).
Global AAM signals are still relatively weak and mixed (ex., the mountain torque). There are still regions particularly across the Southern Hemisphere where zonal mean contributions are large particularly from the frictional and possibly the Coriolis torques. Based on the reanalysis data plots through September 10th, global tropospheric relative AAM is ~minus 1 sigma below the 1968-1997 climatology and a bit lower based on the 1979-1998 climatology. The global tendency has become slightly negative with much of that coming from the subtropical atmosphere of both hemispheres and the northern midlatitudes. A time-latitude section of 200mb zonal mean zonal wind anomalies supports this notion, and even shows very weak zonal mean westerly wind anomalies (~2-3m/s) in the equatorial atmosphere. I feel I can link the former with the Indian Ocean forcing and the latter with the date line convection. Speaking for the Asia-North American sector, this is why we are seeing breaking anticyclones across the North Pacific with accelerating westerly flow farther south.
To summarize, I think we have 1) a weak warm ENSO event, 2) a convectively coupled dynamical signal across the Indian Ocean weakly projecting onto a MJO, and 3) a lot of noise including that given by at least 2 areas of tropical convective forcing. There is also an on-going sub-monthly mountain-frictional torque index cycle (not discussed). We also need to think about the role of the seasonal cycle as we transition into boreal autumn, which also adds a huge source of uncertainty. I do think that GSDM Stage 1 best describes the current weather-climate situation.
So, where does the atmosphere go from here? Uncertainty remains as high as it gets. I do think there is some possibility for at least a convectively coupled Kelvin wave to propagate into the western Pacific adding some enhancement to the tropical convection in that region by the end of week 2. It would be most probable for any MJO component to propagate northeast (seasonal cycle) through the Bay of Bengal into the Tropical Northwest Pacific during week 2 and/or week 3. Hence we may observe enhanced tropical convection from the date line to far Southeast Asia by the end of week 2, shifting east week 3 (?). While all this is going on, tropical convection may continue to “hang out” across the equatorial Indian Ocean (SSTs may become at least temporarily to cool to support thunderstorm clusters) perhaps not as intense as what may be occurring across the Northwest Pacific by then. A thought would be to offer GSDM Stage 1 for week 1, transitioning to GSDM Stage 2 for weeks 2-3. Yes, we may see the North Pacific Jet “outrun” the convection anytime (adds more uncertainty).
I also need to add that, on average, the most intense tropical convective forcing could remain across the Indian Ocean during the next few months, which could “affect” any further development of our weak warm ENSO. To me, it will be critical to see how all this tropical forcing possibly becomes more coherent as transition from boreal autumn to winter occurs.
Week 1 (14-20 September 2006): GSDM Stage 1 is most probable. Like nearly all the models show, 1-2 strong mobile synoptic baroclinic troughs digging into the western part of the country then heading east (in a very complicated flow – I cannot talk about “everything” in these postings) is probable. Portions of the Northern Rockies are likely to experience their first heavy snowfall for this upcoming cold season while severe local storms are probable on the Plains. While temperatures change to much colder than normal across the western states, much of the east and Deep South will keep summertime. The Tropical North Atlantic will need to be monitored for any additional cyclone formation. Right now conditions for tropical cyclogenesis there may be the most favorable thus far for 2006. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (21-27 September 2006): A transition to GSDM Stage 2 may be most probable, meaning an eastward shift of the week 1 pattern across the USA. The trough position may be become established ~95-100W with the ridge just off the west coast into Alaska. Synoptic features would be expected to modulate this pattern.
Week 3 (28-04 October 2006): Persistence of GSDM Stage 2, otherwise unclear.
Once again Southwest Kansas is on the “fence” with a southwest flow storm track. However, there will be a STJ interacting with the strong mobile troughs, and opportunities for some rainfall and storms should exist week 1. The better opportunities will be to our north and east. For weeks 2-3, with a trough axis possibly near or just east of us, we may have a situation of “relatively cool dry northwest flow”. However, individual synoptic systems may shift the trough far enough west to give opportunities of rainfall. Finally, closed lows across the southwest states may also become more probable over the next few weeks interacting with the STJ. This may also be favorable for precipitation across Southwest Kansas.
It is unlikely I will be able to do another posting until about the middle of next week (roughly Tuesday-Wednesday 9/19-20).
Ed Berry
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
Global tropical SSTs remain quite warm across the Western Hemisphere and the western/central Indian Ocean, with the greatest positive anomalies around the equatorial date line and the Eastern Pacific cold tongue. Magnitudes in the latter areas were at least plus 2C. In addition, the entire equatorial basin from ~160E to the west coast of South America has observed weekly mean (September 3-9, 2006) positive SST anomalies of ~1-2C. The latest 5-day averaged TAO buoy array data indicates anomalies up to plus 4C around 140W on the equator at 100m depth, with plus 1-2C anomalies common at depths of 100m east of the date line.
Anomalies of roughly plus .5-1.5C were still present across the Atlantic and much of the Indian Ocean. Below normal SSTs ~minus 1-2C continue around Indonesia, particularly south of the equator to the west coast of Australia. A thought is that the combination of cross-equatorial southerly flow linked to Southern Hemisphere cold outbreaks and upwelling has led to these cool anomalies. Hence we see a pattern of generally a “warm Indian Ocean-cool Indonesian region-warm date line region” in regard to SSTAs, typical of a mature warm ENSO event.
During much of the boreal summer, westerly wind anomalies and even actual westerlies have been common particularly along the equatorial date line region, leading to a deepening of the oceanic thermocline along the equatorial cold tongue (discussed above). However, during the last 5-10 days these westerly anomalies have weakened considerably with even weak easterly anomalies. More said about this below.
Actual SSTs in excess of 29C (threshold we use to maintain significant tropical convective forcing) remain present across portions of the Indian Ocean, and especially the equatorial date line and regions of the Caribbean. These SSTs are most extensive from ~150E-180 within 10 degrees of the equator (see links for further details).
Per the latest ENSO diagnostic discussion dated September 13th, 2006, “El Niño conditions have developed and are likely to continue into early 2007” (please see link below). I would agree with that, and only confirms some of the scientific issues discussed in past writings on this Blog. I sincerely applaud CPC for being proactive to get this information out to everyone!!
Nevertheless, I hope to make the point that the magnitude (and duration) of this event as we go into boreal winter, including global impacts, are unclear (understanding other signals such as trends and what statistics offer). There has been a lot of complicated random (stochastic) forcing going on in the coupled atmosphere-ocean system since at least April 2006. Some of these behaviors have been detailed in our latest weather-climate discussion (link above), and are outstanding research issues (let alone using these kind of notions to make predictions). Right now, only careful weather-climate monitoring within the GSDM framework offers any “hope” of catching these kind of complicated highly non-linear dynamical behaviors in real-time.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
From monitoring, I do feel that the events leading to the onset of weak warm event conditions across the equatorial Pacific Ocean has had at least “episodic impacts” to the global weather during boreal summer. These include general suppression (thus far) of the Tropical North Atlantic tropical cyclone season (understanding climatology and the situation right now), the increase of Tropical Northwest Pacific tropical cyclones (ex., southeast China), the excessive heat much of the USA has dealt with, and the recent change to a cooler and wetter weather pattern for many locations across the Great Plains. The important point to make is there are always forcing-response-feedbacks going on within the Earth-atmosphere-ocean system, and care needs to be offered to thinking that, “some kind of an event is too weak to have an impact”. While there is some truth to these kind of statements statistically (on average), from a weather-climate linkage point of view these notions can lead to difficulty when trying to capture the possibility of extreme weather events. Even on a case by case basis, statistically useful information can be offered for the latter when use of the appropriate framework is employed.
In contrast to the past few months (at least), there are actually at least a couple of weather-climate linkage signals to discuss. The flare-up across the equatorial Indian Ocean (linked to Rossby wave energy dispersions from the North Atlantic) discussed early last week has evolved into a convectively coupled mode at least weakly projecting onto a Madden-Julian Oscillation (MJO). Latest weakly mean OLR anomalies centered ~5-10N/70E were around minus 50-70W/m**2, and a rough calculation gives a phase speed for eastward movement of 5m/s (~4 deg long/day) for this feature (there is also a component moving northeast through India and the Bay of Bengal). The Wheeler phase space plot also lends some support to an MJO. The coherent modes modes Hovmollers show a very weak MJO projection, and also a Kelvin wave emanating to the east. Latest satellite imagery suggests the core of this tropical convective forcing centered ~5-10N/95E, with a Kelvin wave signature moving east along the equator.
There is also a second, less concentrated and weaker area of tropical convective forcing centered along and just north of the date line being forced by the very warm SSTs (discussed above) and other processes. A third (and even weaker) region exists across the Tropical Northeast Pacific. Loosely (for brevity) these last two regions represent an ENSO signal. The forcing across the Tropical North Atlantic and Africa is not well organized.
Now we come to the punch line of this posting that I hope to make clear. We have the convectively coupled dynamical forcing signal over the Indian Ocean and the SST boundary forcing around the date line of the central Pacific Ocean. That is, two areas of tropical forcing, and has been a behavior generally observed since early 2002 (global warming signal?). Which area (ocean) is going to dominate as we go into boreal winter? Obviously there are seasonal cycle considerations and perhaps that may be all we are seeing. Recall that the SSTs are warm across both regions of forcing, with the date line being the warmest where there has been less cloud cover and rainfall recently. Some brief thoughts follow.
Per animations of 150mb and 250mb daily mean vector wind anomalies along with additional tools such as Hovmollers of 250mb meridional wind anomalies, anomalous circulation features have reversed across the subtropical Eastern Hemisphere during the last week. There are now twin anomalous (~10-20m/s, at least) upper tropospheric subtropical anticyclones across the western Indian Ocean and downstream twin cyclones across Indonesia (forced by the divergent outflow) with gyres of the opposite sense in the lower troposphere (leading to some resumption of surface easterly wind anomalies at the date line). This is the expected baroclinic response from a convectively coupled mode such as a MJO.
Impacts onto the extratropics of both hemispheres from the Indian Ocean forcing are currently quite robust. As I type an intense Rossby wave energy dispersion is arcing from this tropical forcing across the North Pacific rim leading to the western USA trough that the numerical models are predicting for the next several days.
Impacts from the date line tropical convection are less robust. Twin subtropical anticyclones continue to appear “off and on”, and have contributed to the subtropical jet (STJ) currently extending into the Desert Southwest. The point is the Indian Ocean tropical forcing is currently dominating the global tropical/subtropical circulation (loosely).
Global AAM signals are still relatively weak and mixed (ex., the mountain torque). There are still regions particularly across the Southern Hemisphere where zonal mean contributions are large particularly from the frictional and possibly the Coriolis torques. Based on the reanalysis data plots through September 10th, global tropospheric relative AAM is ~minus 1 sigma below the 1968-1997 climatology and a bit lower based on the 1979-1998 climatology. The global tendency has become slightly negative with much of that coming from the subtropical atmosphere of both hemispheres and the northern midlatitudes. A time-latitude section of 200mb zonal mean zonal wind anomalies supports this notion, and even shows very weak zonal mean westerly wind anomalies (~2-3m/s) in the equatorial atmosphere. I feel I can link the former with the Indian Ocean forcing and the latter with the date line convection. Speaking for the Asia-North American sector, this is why we are seeing breaking anticyclones across the North Pacific with accelerating westerly flow farther south.
To summarize, I think we have 1) a weak warm ENSO event, 2) a convectively coupled dynamical signal across the Indian Ocean weakly projecting onto a MJO, and 3) a lot of noise including that given by at least 2 areas of tropical convective forcing. There is also an on-going sub-monthly mountain-frictional torque index cycle (not discussed). We also need to think about the role of the seasonal cycle as we transition into boreal autumn, which also adds a huge source of uncertainty. I do think that GSDM Stage 1 best describes the current weather-climate situation.
So, where does the atmosphere go from here? Uncertainty remains as high as it gets. I do think there is some possibility for at least a convectively coupled Kelvin wave to propagate into the western Pacific adding some enhancement to the tropical convection in that region by the end of week 2. It would be most probable for any MJO component to propagate northeast (seasonal cycle) through the Bay of Bengal into the Tropical Northwest Pacific during week 2 and/or week 3. Hence we may observe enhanced tropical convection from the date line to far Southeast Asia by the end of week 2, shifting east week 3 (?). While all this is going on, tropical convection may continue to “hang out” across the equatorial Indian Ocean (SSTs may become at least temporarily to cool to support thunderstorm clusters) perhaps not as intense as what may be occurring across the Northwest Pacific by then. A thought would be to offer GSDM Stage 1 for week 1, transitioning to GSDM Stage 2 for weeks 2-3. Yes, we may see the North Pacific Jet “outrun” the convection anytime (adds more uncertainty).
I also need to add that, on average, the most intense tropical convective forcing could remain across the Indian Ocean during the next few months, which could “affect” any further development of our weak warm ENSO. To me, it will be critical to see how all this tropical forcing possibly becomes more coherent as transition from boreal autumn to winter occurs.
Week 1 (14-20 September 2006): GSDM Stage 1 is most probable. Like nearly all the models show, 1-2 strong mobile synoptic baroclinic troughs digging into the western part of the country then heading east (in a very complicated flow – I cannot talk about “everything” in these postings) is probable. Portions of the Northern Rockies are likely to experience their first heavy snowfall for this upcoming cold season while severe local storms are probable on the Plains. While temperatures change to much colder than normal across the western states, much of the east and Deep South will keep summertime. The Tropical North Atlantic will need to be monitored for any additional cyclone formation. Right now conditions for tropical cyclogenesis there may be the most favorable thus far for 2006. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (21-27 September 2006): A transition to GSDM Stage 2 may be most probable, meaning an eastward shift of the week 1 pattern across the USA. The trough position may be become established ~95-100W with the ridge just off the west coast into Alaska. Synoptic features would be expected to modulate this pattern.
Week 3 (28-04 October 2006): Persistence of GSDM Stage 2, otherwise unclear.
Once again Southwest Kansas is on the “fence” with a southwest flow storm track. However, there will be a STJ interacting with the strong mobile troughs, and opportunities for some rainfall and storms should exist week 1. The better opportunities will be to our north and east. For weeks 2-3, with a trough axis possibly near or just east of us, we may have a situation of “relatively cool dry northwest flow”. However, individual synoptic systems may shift the trough far enough west to give opportunities of rainfall. Finally, closed lows across the southwest states may also become more probable over the next few weeks interacting with the STJ. This may also be favorable for precipitation across Southwest Kansas.
It is unlikely I will be able to do another posting until about the middle of next week (roughly Tuesday-Wednesday 9/19-20).
Ed Berry
Tuesday, September 05, 2006
Next Chapter of the New World Atmosphere – Randomness Rules!!!
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006, has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
The distribution of global tropical SSTs have remained fairly persistent during the last couple of weeks. Western Hemisphere tropical Pacific SSTs remain above normal, with weekly mean anomalies (8/20-26) ~plus 1-2C. The largest magnitudes were centered near the equatorial date line and just west of South America, where daily mean anomalies close to plus 3C were observed on September 4th for the latter (seasonal cycle of SSTs contributing). Anomalies of roughly plus .5-1.5C were still present across the Atlantic and much of the Indian Ocean. Below normal SSTs ~minus 1-2C continue around Indonesia, particularly south of the equator. Hence we see a pattern of a “warm Indian Ocean-cool Indonesian region-warm date line region” in regard to SSTAs, typical of a mature warm ENSO event.
Persistent westerly wind anomalies (~3-5 m/s from about 140E-180) and even actual westerlies have continued to deepen the oceanic thermocline along the equatorial cold tongue. In fact, latest TAO buoy data show anomalies ~plus 4C at 100m depth ~140W, and I may be able to make the case for 2 oceanic Kelvin waves currently propagating east along the cold tongue thermocline.
Actual SSTs in excess of 29C (threshold we use to maintain significant tropical convective forcing) remain present across portions of the Indian Ocean, equatorial date line and regions of the Caribbean. These SSTs are most extensive from ~150E-180 within 10 degrees of the equator (see links for details). An important point is SST boundary forcing has been contributing to multiple regions of enhanced tropical convection, with episodic flare-ups particularly across the Indian Ocean and date line areas during the past several weeks. This has masked any real coherent signals of tropical forcing that may still exist, and for all intents and purposes there is no MJO signal, nor any more modes of 30 and 50-day processes. Much of the tropical forcing is random with little organization.
This is interesting since the spatial distribution of global tropical SSTs may not be random, but slowly evolving in a coherent manner. I have a thought that as the seasonal (southward) migration of tropical convection occurs west of the date line; perhaps by the December 2006-January 2007 time frame SST boundary forced convection in the region of the date line may start to dominate. A secondary region may also continue across the Indian Ocean. This evolution would be consistent with the onset of a mature phase of a warm event. Again, I reiterate that I think the atmosphere is tilting toward a warm ENSO event (magnitude unclear), and some indices would offer a weak warm event has already emerged. What I stated above is pure speculation which I cannot defend at this time. The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
From monitoring, I do think this developing situation (possible warm ENSO) has had at least “episodic impacts” to the global weather during boreal summer. These include general suppression (thus far) of the Tropical North Atlantic (TNA) tropical cyclone season (understanding climatology), the increase of Tropical Northwest Pacific (TNWP) tropical cyclones (ex., southeast China), and the excessive heat much of the USA has dealt with.
Obviously weather-climate linkage signals are very weak. There are interactions which are certainly not linear and random that has been occurring for a while, and I only want to summarize the (hopefully) important behaviors for brevity. Right now I think the most robust tropical convective signal is emerging across the equatorial Indian Ocean (OLRA ~ minus 50-70 W/m**2), and I think Rossby wave energy dispersion (RWD) processes moving through the North Atlantic/Scandinavia are contributing. Other regions remain north of the date line, around the Americas and finally the TNA into Africa. Various plots of velocity potential suggest the latter is a convectively coupled dynamical signal which may emerge into the Indian Ocean during the next week or so.
The tropical convection across the Indian Ocean is linked with upper tropospheric westerlies (see animations of 150mb and 250mb daily mean vector wind anomalies), perhaps suggestive of extratropical dynamical forcing. The coherent modes Hovmoller plots suggest a convectively coupled Kevin wave to develop from this enhanced rainfall and move east. My own thought would support that notion, possibly leading to increased enhancement of tropical convection from the date line region toward the Philippines sometime during week 2. Convection may also remain enhanced across the Indian Ocean as the weak dynamical signal comes into the Eastern Hemisphere. Models such as the CDC and NCEP ensemble maintain precipitation across these 2 areas during week 2 largely responding to the SSTs.
Per animations of 150mb and 250mb daily mean vector wind anomalies, around September 2nd nearly symmetric RWDs linked to twin subtropical anticyclones ~120E occurred in both hemispheres. Circulation anomalies were roughly 20-30m/s at 150mb. The Northern Hemisphere version went across the Pacific Rim and lead to the anomalous cyclone that was across the Northern Plains while its counterpart led to a significant cold outbreak across much of South America. This pattern has dispersed, with currently a lot of northeast-southwest tilt (AAM transport signals were still weak 3 days ago per reanalysis data) to the anomalies from Asia to North America. There is a “hint” that the twin anomalous subtropical anticyclones are currently shifting west toward the Indian Ocean convection. Finally I should mention that twin anticyclones (with generally weak anomalies) keep “coming and going” around the equatorial date line region. The latter is likely a warm ENSO signal.
Global AAM signals are much too weak to discuss. There are regions particularly across the Southern Hemisphere where zonal mean contributions are large particularly from the frictional and possibly the Coriolis torques. Based on the reanalysis data plots through September 2nd, global tropospheric relative AAM is ~minus 1 sigma below the 1968-1997 climatology.
A time-latitude section of 200mb zonal mean zonal wind anomalies can give some sense (this is only 1 level verses a zonally and vertically averaged quantity) as to how global relative AAM is being distributed. Loosely, during the past week zonal mean westerly wind anomalies (magnitudes ~10m/s) have dominated the extratropics poleward of 50 degrees of both hemispheres. Weak easterlies have been present across the equatorial and subtropical atmosphere of the Southern Hemisphere and midlatitudes of the Northern Hemisphere. Finally, weak zonal mean westerly wind anomalies are present across the subtropical atmosphere of the Northern Hemisphere. The latter are contributing to a split-flow pattern from the Pacific into North America, and a recent positive AAM tendency along the equator of ~2 Hadleys may have assisted. As anyone can now see, this situation is a mess, and if the reader looks at the plot reference above, my description does not do the complexity justice.
To summarize, I think we have a weather-climate situation consisting of 1) a likely emerging warm event, 2) a convective signal emerging in the Indian Ocean, and 3) mostly noise. We also need to think about the role of the seasonal cycle as transition to boreal autumn approaches, which also adds a huge source of uncertainty.
Signals are simply too weak to “fit in” to the GSDM framework. From spending lots of hours studying animations of various fields, AAM plots, Hovmollers of “everything”, many ensemble prediction schemes, diagnostics from other worldwide meteorological centers, etc., my suspicion would be to see an emergence to GSDM Stage 2 sometime during the next 1-3 weeks. A key observation will be to watch for a rapid increase in the tropical convection from around the date line to near Southeast Asia during the next few weeks (along with a strong positive maximum in AAM tendency).
Initially troughs may amplify across the western USA with a ridge over the Deep South. Should we see a mature GSDM Stage 2 there would be a large amplitude ridge from ~130W into Alaska with an anomalously deep trough across the middle of North America. This would suggest dry/warm for the far western states and a tilt toward cool/wet for roughly the eastern half of the country. I am not going to make any attempt to break down this possibility week by week. Like it or not, this is the reality we are currently dealing with in regard to making any kind of weather forecast in our situation. Confidence is as low as it gets and any useful probabilistic statements must indicate that.
Week 1 (6-12 September 2006): See above. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (13-19 September 2006): Same as week 1.
Week 3 (20-26 September 2006): Same as week 1.
In general I think we are looking at cooler than normal temperatures with some opportunities
for rainfall through at least week 1 for Southwest Kansas. Afterwards, unclear.
It is unlikely I will be able to do another posting until about the middle of next week (roughly Wednesday, 9/13). Maybe signals will become clearer by then!
Ed Berry
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006, has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
The distribution of global tropical SSTs have remained fairly persistent during the last couple of weeks. Western Hemisphere tropical Pacific SSTs remain above normal, with weekly mean anomalies (8/20-26) ~plus 1-2C. The largest magnitudes were centered near the equatorial date line and just west of South America, where daily mean anomalies close to plus 3C were observed on September 4th for the latter (seasonal cycle of SSTs contributing). Anomalies of roughly plus .5-1.5C were still present across the Atlantic and much of the Indian Ocean. Below normal SSTs ~minus 1-2C continue around Indonesia, particularly south of the equator. Hence we see a pattern of a “warm Indian Ocean-cool Indonesian region-warm date line region” in regard to SSTAs, typical of a mature warm ENSO event.
Persistent westerly wind anomalies (~3-5 m/s from about 140E-180) and even actual westerlies have continued to deepen the oceanic thermocline along the equatorial cold tongue. In fact, latest TAO buoy data show anomalies ~plus 4C at 100m depth ~140W, and I may be able to make the case for 2 oceanic Kelvin waves currently propagating east along the cold tongue thermocline.
Actual SSTs in excess of 29C (threshold we use to maintain significant tropical convective forcing) remain present across portions of the Indian Ocean, equatorial date line and regions of the Caribbean. These SSTs are most extensive from ~150E-180 within 10 degrees of the equator (see links for details). An important point is SST boundary forcing has been contributing to multiple regions of enhanced tropical convection, with episodic flare-ups particularly across the Indian Ocean and date line areas during the past several weeks. This has masked any real coherent signals of tropical forcing that may still exist, and for all intents and purposes there is no MJO signal, nor any more modes of 30 and 50-day processes. Much of the tropical forcing is random with little organization.
This is interesting since the spatial distribution of global tropical SSTs may not be random, but slowly evolving in a coherent manner. I have a thought that as the seasonal (southward) migration of tropical convection occurs west of the date line; perhaps by the December 2006-January 2007 time frame SST boundary forced convection in the region of the date line may start to dominate. A secondary region may also continue across the Indian Ocean. This evolution would be consistent with the onset of a mature phase of a warm event. Again, I reiterate that I think the atmosphere is tilting toward a warm ENSO event (magnitude unclear), and some indices would offer a weak warm event has already emerged. What I stated above is pure speculation which I cannot defend at this time. The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
From monitoring, I do think this developing situation (possible warm ENSO) has had at least “episodic impacts” to the global weather during boreal summer. These include general suppression (thus far) of the Tropical North Atlantic (TNA) tropical cyclone season (understanding climatology), the increase of Tropical Northwest Pacific (TNWP) tropical cyclones (ex., southeast China), and the excessive heat much of the USA has dealt with.
Obviously weather-climate linkage signals are very weak. There are interactions which are certainly not linear and random that has been occurring for a while, and I only want to summarize the (hopefully) important behaviors for brevity. Right now I think the most robust tropical convective signal is emerging across the equatorial Indian Ocean (OLRA ~ minus 50-70 W/m**2), and I think Rossby wave energy dispersion (RWD) processes moving through the North Atlantic/Scandinavia are contributing. Other regions remain north of the date line, around the Americas and finally the TNA into Africa. Various plots of velocity potential suggest the latter is a convectively coupled dynamical signal which may emerge into the Indian Ocean during the next week or so.
The tropical convection across the Indian Ocean is linked with upper tropospheric westerlies (see animations of 150mb and 250mb daily mean vector wind anomalies), perhaps suggestive of extratropical dynamical forcing. The coherent modes Hovmoller plots suggest a convectively coupled Kevin wave to develop from this enhanced rainfall and move east. My own thought would support that notion, possibly leading to increased enhancement of tropical convection from the date line region toward the Philippines sometime during week 2. Convection may also remain enhanced across the Indian Ocean as the weak dynamical signal comes into the Eastern Hemisphere. Models such as the CDC and NCEP ensemble maintain precipitation across these 2 areas during week 2 largely responding to the SSTs.
Per animations of 150mb and 250mb daily mean vector wind anomalies, around September 2nd nearly symmetric RWDs linked to twin subtropical anticyclones ~120E occurred in both hemispheres. Circulation anomalies were roughly 20-30m/s at 150mb. The Northern Hemisphere version went across the Pacific Rim and lead to the anomalous cyclone that was across the Northern Plains while its counterpart led to a significant cold outbreak across much of South America. This pattern has dispersed, with currently a lot of northeast-southwest tilt (AAM transport signals were still weak 3 days ago per reanalysis data) to the anomalies from Asia to North America. There is a “hint” that the twin anomalous subtropical anticyclones are currently shifting west toward the Indian Ocean convection. Finally I should mention that twin anticyclones (with generally weak anomalies) keep “coming and going” around the equatorial date line region. The latter is likely a warm ENSO signal.
Global AAM signals are much too weak to discuss. There are regions particularly across the Southern Hemisphere where zonal mean contributions are large particularly from the frictional and possibly the Coriolis torques. Based on the reanalysis data plots through September 2nd, global tropospheric relative AAM is ~minus 1 sigma below the 1968-1997 climatology.
A time-latitude section of 200mb zonal mean zonal wind anomalies can give some sense (this is only 1 level verses a zonally and vertically averaged quantity) as to how global relative AAM is being distributed. Loosely, during the past week zonal mean westerly wind anomalies (magnitudes ~10m/s) have dominated the extratropics poleward of 50 degrees of both hemispheres. Weak easterlies have been present across the equatorial and subtropical atmosphere of the Southern Hemisphere and midlatitudes of the Northern Hemisphere. Finally, weak zonal mean westerly wind anomalies are present across the subtropical atmosphere of the Northern Hemisphere. The latter are contributing to a split-flow pattern from the Pacific into North America, and a recent positive AAM tendency along the equator of ~2 Hadleys may have assisted. As anyone can now see, this situation is a mess, and if the reader looks at the plot reference above, my description does not do the complexity justice.
To summarize, I think we have a weather-climate situation consisting of 1) a likely emerging warm event, 2) a convective signal emerging in the Indian Ocean, and 3) mostly noise. We also need to think about the role of the seasonal cycle as transition to boreal autumn approaches, which also adds a huge source of uncertainty.
Signals are simply too weak to “fit in” to the GSDM framework. From spending lots of hours studying animations of various fields, AAM plots, Hovmollers of “everything”, many ensemble prediction schemes, diagnostics from other worldwide meteorological centers, etc., my suspicion would be to see an emergence to GSDM Stage 2 sometime during the next 1-3 weeks. A key observation will be to watch for a rapid increase in the tropical convection from around the date line to near Southeast Asia during the next few weeks (along with a strong positive maximum in AAM tendency).
Initially troughs may amplify across the western USA with a ridge over the Deep South. Should we see a mature GSDM Stage 2 there would be a large amplitude ridge from ~130W into Alaska with an anomalously deep trough across the middle of North America. This would suggest dry/warm for the far western states and a tilt toward cool/wet for roughly the eastern half of the country. I am not going to make any attempt to break down this possibility week by week. Like it or not, this is the reality we are currently dealing with in regard to making any kind of weather forecast in our situation. Confidence is as low as it gets and any useful probabilistic statements must indicate that.
Week 1 (6-12 September 2006): See above. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (13-19 September 2006): Same as week 1.
Week 3 (20-26 September 2006): Same as week 1.
In general I think we are looking at cooler than normal temperatures with some opportunities
for rainfall through at least week 1 for Southwest Kansas. Afterwards, unclear.
It is unlikely I will be able to do another posting until about the middle of next week (roughly Wednesday, 9/13). Maybe signals will become clearer by then!
Ed Berry
Saturday, August 26, 2006
Next Update ~9/6/2006
As I stated in my last posting, it is unlikely I will be able to do another
discussion until around September 6th. I hope weather-climate signals
will become clearer by then. Right now the atmosphere is behaving
randomly, with some effort to reorganize the tropical convective forcing
back into the Eastern Hemisphere. Perhaps the global circulation is
headed for GSDM Stage 1 in the near future. Stay tuned!!!
Ed Berry
discussion until around September 6th. I hope weather-climate signals
will become clearer by then. Right now the atmosphere is behaving
randomly, with some effort to reorganize the tropical convective forcing
back into the Eastern Hemisphere. Perhaps the global circulation is
headed for GSDM Stage 1 in the near future. Stay tuned!!!
Ed Berry
Wednesday, August 23, 2006
New World Atmosphere Rocks!!!
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006, has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
Western Hemisphere tropical Pacific SSTs remain above normal, with weekly mean anomalies (8/13-19) ~plus 1-1.5C. Somewhat larger anomalies exist just west of South America and from the equatorial date line to about 160E, with magnitudes ~plus 2C. SST anomalies ~plus .5-1.5C were also prevalent across most of the Caribbean and portions of the Tropical North Atlantic (TNA), as well as the Indian Ocean. Actual SSTs in excess of 29C are present across portions of the Indian Ocean, equatorial date line and regions of the Caribbean. Below normal SSTs, with anomalies ~minus .5-1.0C have been observed for a few weeks from ~90-150E particularly just south of the equator around Indonesia to north of Australia. This pattern of cool SSTs near Indonesia with warmth around the date line is typical of mature warm events, not developing ones which may presently be the case.
TAO buoy array and other data continue to tell us of persistent strong westerly wind anomalies (and actual westerlies) on the equator at the date line (anomalies ~5-10m/s), with SSTAs ~plus 2C down to depths of 150m in that region. In fact, there may be 2 downwelling oceanic Kelvin waves moving along the thermocline of the equatorial Pacific cold tongue, with one just east of the date line and the other ~120W. To me, all indications are that the ocean-atmosphere system is tilting toward a warm ENSO event (magnitude unclear), and some indices would offer a weak warm event has already emerged.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
From monitoring, I do think this developing situation (possible warm ENSO) has had at least “episodic impacts” the global weather during boreal summer. These include suppression (thus far) of the TNA tropical cyclone season (understanding climatology), the increase of TNWP tropical cyclones (ex., southeast China), and the excessive heat much of the USA has dealt with.
Weather-climate linkage signals particularly from the tropics remain very weak. There is evidence, as would be expected per above, that atmosphere-ocean coupling between the SST boundary forced tropical convection west of the date line and circulation response/feedback has been occurring possibly since April (see recent weather-climate discussion for details). However, the MJO signal is virtually non-existent and even the ~50-day and ~30-day tropical forcing signals are anemic at best. The AAM plots, particularly the tendency and mountain and frictional torques still do give some evidence of the latter. There is a fast convective dynamical signal (weakly projects onto a Kelvin wave per Coherent modes Hovmollers) moving through the Western Hemisphere at ~16-17m/s located at about 40W. It is possible this signal will emerge into the Indian Ocean by the end of week 1, especially since thunderstorm clusters are becoming very active across central Africa.
Per animations of 150mb and 250mb daily mean vector wind anomalies (and other fields) I can offer that the tropical convective flare-up ~August 7-10 at roughly 160E first impacted the extratropics via Rossby wave energy dispersions (and other complex processes), and currently the extratropics may be forcing back into the tropics. For instance, about a week after the flare-up blocking appeared across the North Atlantic which subsequently dispersed into northern Asia and led to a recent anticyclonic wave breaking (AWB) event across the Northwest Pacific. During this whole period anomalous equatorial zonal mean westerly flow collapsed with even weak zonal mean easterlies appearing. Additionally, the AWB has also assisted with AAM transport to allow zonal mean westerly flow (anomalies ~plus 5m/s at 200mb) to propagate poleward to ~25N. There have been at least 2 weather impacts (relevant to the USA): 1) a more favorable environment for TNA tropical cyclogenesis, and 2) enhancement of the southwest USA monsoon.
There may be another important repercussion: extratropical feedbacks into the tropics to further develop a possible oncoming warm event. I can also offer that the above discussed AWB, through extratropical baroclinic processes interacting with dynamical processes in the tropics, have allowed for the persistence and even intensification of the anomalous equatorial westerlies near the date line. All of this is very speculative and needs to quantified for any hope of defensibility. Whatever the case may be, the atmosphere is on a path which is presenting tremendous difficulty to diagnose using “conventional thinking” (not to say things like the above have not happened before; they have).
There are also active tropical convective signals rapidly appearing across both the west central Pacific (which has been a region of recent suppression) and equatorial Indian Ocean. Strong convective suppression still continues from ~80-120E. The recent active signals appear to have had assistance from the Southern Hemisphere extratropics. I would speculate that the Indian Ocean convection may propagate northeast toward the Bay of Bengal and Southeast Asia, possibly consolidating the growing convection across the TNWP during the next few weeks. One could also offer 2 separate areas may persist for “a while” given the SSTs and the fast dynamical signal currently moving through the Western Hemisphere.
To summarize, I think we have a weather-climate situation consisting of 1) a likely emerging warm event, 2) fast Western Hemisphere convectively coupled dynamical signal about to propagate into the Eastern Hemisphere, and 3) a lot of weak unclear speculative signals as discussed above, which is seemingly a situation becoming “the norm”. We also need to think about the role of the seasonal cycle as transition to boreal autumn approaches.
The AAM plots present little global signal. There are strong AAM signals from the Southern Hemisphere particularly from the frictional and Coriolis torques, and earth components contributing to a global relative AAM signal of ~minus ½ sigma. Since about June 1st, zonal mean westerly flow at 200mb has been well above average from 25-40S with anomalies as great as 15-20m/s, allowing for a very active storm track there. The latter may also be a warm ENSO signal.
GSDM Stage 3-4 best describes the current weather-climate situation (considering the AAM budget). Zonal mean anomalous westerly flow is propagating well into northern subtropical atmosphere, while weak zonal mean easterly flow replaces it along the equator. Also, tropical convective forcing across the Eastern Hemisphere appears to be on the increase. I did not expect this situation a week ago. My thoughts were for GSDM Stage 2 at this time, and any I prediction I based on that was a poor assessment. For instance, I had thoughts of a fairly cool airmass for the middle of the USA starting this weekend into next week, and that does not look likely (there will still be a polar Pacific airmass moving into the Plains).
Where we go from here is unclear. Given there are 2 areas of tropical forcing emerging across the Eastern Hemisphere, past experience would tell me GSDM Stage 4-1 for week 1. The ECMWF deterministic run through day 7 supports this notion. Models such as the NCEP GFS 500mb ensemble mean suggest a GSDM Stage 3 like circulation for week 2. My humble thought would be to speculate a convective signal to propagate into the TNWP by the end of week 2 or week 3, perhaps leading to GSDM Stage 2 during that time. Whatever the case, careful daily monitoring within the GSDM framework will be needed to capture the possibility of a significant signal emerging from what is essentially mostly noise.
The numerical models have also been struggling with this situation. While these numerical prediction schemes have little information about the impact of tropical convective forcing after about day 5, they do take into account non-linear feedbacks. My advice to anyone having to make predictions is to consult as many numerical ensemble prediction schemes as possible. That, along with monitoring using the GSDM, should give some hope for success for roughly week 1. Confidence in the following outlooks is as low as it gets. I would feel this way even if there was excellent ensemble numerical model agreement through week 3 since I can point to sources of uncertainty with the GSDM framework that numerical models will struggle with.
Week 1 (24-30 August 2006): GSDM Stage 4-1 may be most probable, meaning a subtropical ridge across the Deep Southeast USA and relatively low amplitude NE-SW trough across the western states. The SW USA monsoon should remain quite active. There may be an active MCS storm track across much of the middle of the country. Flooding from heavy rain producing thunderstorms is a concern for much of the Desert Southwest into the Central Plains. A window of opportunity for tropical cyclogenesis should continue across the TNA. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (31 August – 6 September 2006): As seasonal transition to stronger westerly flow continues across the country, loosely GSDM Stage 1-2 may occur. That would suggest more mobile troughs coming into the western USA with a subtropical ridge across the Southeast. The Desert Southwest monsoon may start to weaken. Everything else is unclear.
Week 3 (7-13 September 2006): Unclear to offer anything statistically useful to folks who need it.
Another decent episode of rainfall (including a flooding hazard) is probable for Southwest Kansas at least through this upcoming weekend along with near-below normal temperatures. I can see (with my crystal ball) another scenario for a frontal episode of rainfall late next week; however, upper tropospheric moisture transport from the deep tropics may be less by that time. Temperatures may warm to above normal before this. Climatology will start working against us for rainfall as we get into this fall. We will see. I can always dream up scenarios to work against it.
I will try to do another posting this upcoming weekend. I will be on travel from 8/27-9/2, and the next posting may not be until 9/6.
Ed Berry
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006, has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
Western Hemisphere tropical Pacific SSTs remain above normal, with weekly mean anomalies (8/13-19) ~plus 1-1.5C. Somewhat larger anomalies exist just west of South America and from the equatorial date line to about 160E, with magnitudes ~plus 2C. SST anomalies ~plus .5-1.5C were also prevalent across most of the Caribbean and portions of the Tropical North Atlantic (TNA), as well as the Indian Ocean. Actual SSTs in excess of 29C are present across portions of the Indian Ocean, equatorial date line and regions of the Caribbean. Below normal SSTs, with anomalies ~minus .5-1.0C have been observed for a few weeks from ~90-150E particularly just south of the equator around Indonesia to north of Australia. This pattern of cool SSTs near Indonesia with warmth around the date line is typical of mature warm events, not developing ones which may presently be the case.
TAO buoy array and other data continue to tell us of persistent strong westerly wind anomalies (and actual westerlies) on the equator at the date line (anomalies ~5-10m/s), with SSTAs ~plus 2C down to depths of 150m in that region. In fact, there may be 2 downwelling oceanic Kelvin waves moving along the thermocline of the equatorial Pacific cold tongue, with one just east of the date line and the other ~120W. To me, all indications are that the ocean-atmosphere system is tilting toward a warm ENSO event (magnitude unclear), and some indices would offer a weak warm event has already emerged.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
From monitoring, I do think this developing situation (possible warm ENSO) has had at least “episodic impacts” the global weather during boreal summer. These include suppression (thus far) of the TNA tropical cyclone season (understanding climatology), the increase of TNWP tropical cyclones (ex., southeast China), and the excessive heat much of the USA has dealt with.
Weather-climate linkage signals particularly from the tropics remain very weak. There is evidence, as would be expected per above, that atmosphere-ocean coupling between the SST boundary forced tropical convection west of the date line and circulation response/feedback has been occurring possibly since April (see recent weather-climate discussion for details). However, the MJO signal is virtually non-existent and even the ~50-day and ~30-day tropical forcing signals are anemic at best. The AAM plots, particularly the tendency and mountain and frictional torques still do give some evidence of the latter. There is a fast convective dynamical signal (weakly projects onto a Kelvin wave per Coherent modes Hovmollers) moving through the Western Hemisphere at ~16-17m/s located at about 40W. It is possible this signal will emerge into the Indian Ocean by the end of week 1, especially since thunderstorm clusters are becoming very active across central Africa.
Per animations of 150mb and 250mb daily mean vector wind anomalies (and other fields) I can offer that the tropical convective flare-up ~August 7-10 at roughly 160E first impacted the extratropics via Rossby wave energy dispersions (and other complex processes), and currently the extratropics may be forcing back into the tropics. For instance, about a week after the flare-up blocking appeared across the North Atlantic which subsequently dispersed into northern Asia and led to a recent anticyclonic wave breaking (AWB) event across the Northwest Pacific. During this whole period anomalous equatorial zonal mean westerly flow collapsed with even weak zonal mean easterlies appearing. Additionally, the AWB has also assisted with AAM transport to allow zonal mean westerly flow (anomalies ~plus 5m/s at 200mb) to propagate poleward to ~25N. There have been at least 2 weather impacts (relevant to the USA): 1) a more favorable environment for TNA tropical cyclogenesis, and 2) enhancement of the southwest USA monsoon.
There may be another important repercussion: extratropical feedbacks into the tropics to further develop a possible oncoming warm event. I can also offer that the above discussed AWB, through extratropical baroclinic processes interacting with dynamical processes in the tropics, have allowed for the persistence and even intensification of the anomalous equatorial westerlies near the date line. All of this is very speculative and needs to quantified for any hope of defensibility. Whatever the case may be, the atmosphere is on a path which is presenting tremendous difficulty to diagnose using “conventional thinking” (not to say things like the above have not happened before; they have).
There are also active tropical convective signals rapidly appearing across both the west central Pacific (which has been a region of recent suppression) and equatorial Indian Ocean. Strong convective suppression still continues from ~80-120E. The recent active signals appear to have had assistance from the Southern Hemisphere extratropics. I would speculate that the Indian Ocean convection may propagate northeast toward the Bay of Bengal and Southeast Asia, possibly consolidating the growing convection across the TNWP during the next few weeks. One could also offer 2 separate areas may persist for “a while” given the SSTs and the fast dynamical signal currently moving through the Western Hemisphere.
To summarize, I think we have a weather-climate situation consisting of 1) a likely emerging warm event, 2) fast Western Hemisphere convectively coupled dynamical signal about to propagate into the Eastern Hemisphere, and 3) a lot of weak unclear speculative signals as discussed above, which is seemingly a situation becoming “the norm”. We also need to think about the role of the seasonal cycle as transition to boreal autumn approaches.
The AAM plots present little global signal. There are strong AAM signals from the Southern Hemisphere particularly from the frictional and Coriolis torques, and earth components contributing to a global relative AAM signal of ~minus ½ sigma. Since about June 1st, zonal mean westerly flow at 200mb has been well above average from 25-40S with anomalies as great as 15-20m/s, allowing for a very active storm track there. The latter may also be a warm ENSO signal.
GSDM Stage 3-4 best describes the current weather-climate situation (considering the AAM budget). Zonal mean anomalous westerly flow is propagating well into northern subtropical atmosphere, while weak zonal mean easterly flow replaces it along the equator. Also, tropical convective forcing across the Eastern Hemisphere appears to be on the increase. I did not expect this situation a week ago. My thoughts were for GSDM Stage 2 at this time, and any I prediction I based on that was a poor assessment. For instance, I had thoughts of a fairly cool airmass for the middle of the USA starting this weekend into next week, and that does not look likely (there will still be a polar Pacific airmass moving into the Plains).
Where we go from here is unclear. Given there are 2 areas of tropical forcing emerging across the Eastern Hemisphere, past experience would tell me GSDM Stage 4-1 for week 1. The ECMWF deterministic run through day 7 supports this notion. Models such as the NCEP GFS 500mb ensemble mean suggest a GSDM Stage 3 like circulation for week 2. My humble thought would be to speculate a convective signal to propagate into the TNWP by the end of week 2 or week 3, perhaps leading to GSDM Stage 2 during that time. Whatever the case, careful daily monitoring within the GSDM framework will be needed to capture the possibility of a significant signal emerging from what is essentially mostly noise.
The numerical models have also been struggling with this situation. While these numerical prediction schemes have little information about the impact of tropical convective forcing after about day 5, they do take into account non-linear feedbacks. My advice to anyone having to make predictions is to consult as many numerical ensemble prediction schemes as possible. That, along with monitoring using the GSDM, should give some hope for success for roughly week 1. Confidence in the following outlooks is as low as it gets. I would feel this way even if there was excellent ensemble numerical model agreement through week 3 since I can point to sources of uncertainty with the GSDM framework that numerical models will struggle with.
Week 1 (24-30 August 2006): GSDM Stage 4-1 may be most probable, meaning a subtropical ridge across the Deep Southeast USA and relatively low amplitude NE-SW trough across the western states. The SW USA monsoon should remain quite active. There may be an active MCS storm track across much of the middle of the country. Flooding from heavy rain producing thunderstorms is a concern for much of the Desert Southwest into the Central Plains. A window of opportunity for tropical cyclogenesis should continue across the TNA. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (31 August – 6 September 2006): As seasonal transition to stronger westerly flow continues across the country, loosely GSDM Stage 1-2 may occur. That would suggest more mobile troughs coming into the western USA with a subtropical ridge across the Southeast. The Desert Southwest monsoon may start to weaken. Everything else is unclear.
Week 3 (7-13 September 2006): Unclear to offer anything statistically useful to folks who need it.
Another decent episode of rainfall (including a flooding hazard) is probable for Southwest Kansas at least through this upcoming weekend along with near-below normal temperatures. I can see (with my crystal ball) another scenario for a frontal episode of rainfall late next week; however, upper tropospheric moisture transport from the deep tropics may be less by that time. Temperatures may warm to above normal before this. Climatology will start working against us for rainfall as we get into this fall. We will see. I can always dream up scenarios to work against it.
I will try to do another posting this upcoming weekend. I will be on travel from 8/27-9/2, and the next posting may not be until 9/6.
Ed Berry
Tuesday, August 15, 2006
The New World Atmosphere – Update
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Please see previous posting for links. This writing will be very short, and it is unlikely I will do one this weekend due to covering operational shifts and work to get the next weather-climate discussion out for posting on the ESRL/PSD MJO web site. I should be able to do a complete Blog discussion next Wednesday, 8/22. What I posted on August 12th is still quite valid.
Tropical Ocean SSTs remain above average across most of the Western Hemisphere and the Indian Ocean, with cooler than normal values centered on Indonesia. Actual SSTs in excess of 30C have been observed along and just north of the equator ~160E, with 29C and warmer over the TNWP as well as from the East Pacific, Caribbean into the Gulf of Mexico. Latest TAO data suggests the oceanic Kelvin wave is located around 160W, and that surface westerly wind anomalies (~5m/s) have once again returned to the equatorial date line region.
There continues to be little signal of a MJO, and there is some evidence of weak coupling between the tropical convection and warm SSTs west of the date line. An eastward propagating dynamical signal has emerged into the Western Hemisphere, moving along the East Pacific ITCZ as I type (phase speed ~8-10m/s). Finally, consolidation of tropical forcing is taking place centered ~10-15N/110E (including the monsoon systems), with an intense flare-up just north of the equator centered ~60E.
Consistent with previous events during the last several months, I would expect Indian Ocean flare-up to propagate northeast and also merge with the on-going convective activity from India to Southeast Asia. This whole region of enhancement could easily shift into the TNWP weeks 2-3 maintaining the tropical cyclone concern for that region.
While tropical convection should persist west of the date line (SST boundary forcing), general suppression may be the case around Indonesia, all during weeks 1 and 2. The TNWP forcing could easily reinvigorate the SST boundary forced convection west of the dateline afterwards. Finally, the Western Hemisphere dynamical signal may propagate though the Americas into the Atlantic by weeks 2-3, creating a tropical cyclone hazard for the East Pacific and perhaps the North Atlantic later on. The latter will need careful monitoring, especially for hybrids, particularly if the environment of the deep tropical Atlantic remains unfavorable.
Zonal mean westerly wind anomalies to continue to increase from 15S-25N, with magnitudes at 200mb ~5m/s at 15N. Animations of 150mb and 250mb daily mean vector wind anomalies shows the appearance of twin upper tropospheric anticyclones around the date line within the tropics, with distorted twin subtropical anticyclones ~120E. These anticyclones (with lower tropospheric cyclones – baroclinic processes) are the result of the divergent outflows from the tropical forcing discussed above. The pair at the date line is a response the SST boundary forcing (and perhaps an ENSO signal due to an evolving possible warm event; a slower process than subseasonal), and are contributing to the recent increase of zonal mean anomalous westerly flow throughout the tropical and subtropical atmospheres. I can link the large anticyclonic circulation anomaly just southeast of Greenland to at least once recent rapid Rossby wave energy dispersion (RWD) from the date line anticyclones forced by the SSTs. Some of the anomalous westerly flow is already impacting not only the Tropical North Atlantic, but even enhancing moisture transport into the Desert Southwest of the USA (interacting with the extratropics).
GSDM Stage 1-2 best describes the global circulation (see links to AAM plots). A transition to GSDM Stage 2 would be most probable during week 2, possibly persisting into week 3. Afterwards, offering anything statistically useful is unclear. This would suggest retrogression of the ridge back into the Great Basin and perhaps into Alaska, with a central and eastern North American trough. Responding to some of the initial conditions discussed above, most ensemble numerical models support this notion for week 2. However, uncertainty continues extremely high, and I have been suggesting this option for at least 2 weeks (which has not been a total bust). We have been dealing with an atmosphere having somewhat unusual forcing for at least the past few months, and trying to apply “conventional (linear) thinking” to it. For example, trying to apply MJO reasoning to dynamical processes that are not MJO. Expected weather has already been discussed in previous postings.
Ed Berry
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Please see previous posting for links. This writing will be very short, and it is unlikely I will do one this weekend due to covering operational shifts and work to get the next weather-climate discussion out for posting on the ESRL/PSD MJO web site. I should be able to do a complete Blog discussion next Wednesday, 8/22. What I posted on August 12th is still quite valid.
Tropical Ocean SSTs remain above average across most of the Western Hemisphere and the Indian Ocean, with cooler than normal values centered on Indonesia. Actual SSTs in excess of 30C have been observed along and just north of the equator ~160E, with 29C and warmer over the TNWP as well as from the East Pacific, Caribbean into the Gulf of Mexico. Latest TAO data suggests the oceanic Kelvin wave is located around 160W, and that surface westerly wind anomalies (~5m/s) have once again returned to the equatorial date line region.
There continues to be little signal of a MJO, and there is some evidence of weak coupling between the tropical convection and warm SSTs west of the date line. An eastward propagating dynamical signal has emerged into the Western Hemisphere, moving along the East Pacific ITCZ as I type (phase speed ~8-10m/s). Finally, consolidation of tropical forcing is taking place centered ~10-15N/110E (including the monsoon systems), with an intense flare-up just north of the equator centered ~60E.
Consistent with previous events during the last several months, I would expect Indian Ocean flare-up to propagate northeast and also merge with the on-going convective activity from India to Southeast Asia. This whole region of enhancement could easily shift into the TNWP weeks 2-3 maintaining the tropical cyclone concern for that region.
While tropical convection should persist west of the date line (SST boundary forcing), general suppression may be the case around Indonesia, all during weeks 1 and 2. The TNWP forcing could easily reinvigorate the SST boundary forced convection west of the dateline afterwards. Finally, the Western Hemisphere dynamical signal may propagate though the Americas into the Atlantic by weeks 2-3, creating a tropical cyclone hazard for the East Pacific and perhaps the North Atlantic later on. The latter will need careful monitoring, especially for hybrids, particularly if the environment of the deep tropical Atlantic remains unfavorable.
Zonal mean westerly wind anomalies to continue to increase from 15S-25N, with magnitudes at 200mb ~5m/s at 15N. Animations of 150mb and 250mb daily mean vector wind anomalies shows the appearance of twin upper tropospheric anticyclones around the date line within the tropics, with distorted twin subtropical anticyclones ~120E. These anticyclones (with lower tropospheric cyclones – baroclinic processes) are the result of the divergent outflows from the tropical forcing discussed above. The pair at the date line is a response the SST boundary forcing (and perhaps an ENSO signal due to an evolving possible warm event; a slower process than subseasonal), and are contributing to the recent increase of zonal mean anomalous westerly flow throughout the tropical and subtropical atmospheres. I can link the large anticyclonic circulation anomaly just southeast of Greenland to at least once recent rapid Rossby wave energy dispersion (RWD) from the date line anticyclones forced by the SSTs. Some of the anomalous westerly flow is already impacting not only the Tropical North Atlantic, but even enhancing moisture transport into the Desert Southwest of the USA (interacting with the extratropics).
GSDM Stage 1-2 best describes the global circulation (see links to AAM plots). A transition to GSDM Stage 2 would be most probable during week 2, possibly persisting into week 3. Afterwards, offering anything statistically useful is unclear. This would suggest retrogression of the ridge back into the Great Basin and perhaps into Alaska, with a central and eastern North American trough. Responding to some of the initial conditions discussed above, most ensemble numerical models support this notion for week 2. However, uncertainty continues extremely high, and I have been suggesting this option for at least 2 weeks (which has not been a total bust). We have been dealing with an atmosphere having somewhat unusual forcing for at least the past few months, and trying to apply “conventional (linear) thinking” to it. For example, trying to apply MJO reasoning to dynamical processes that are not MJO. Expected weather has already been discussed in previous postings.
Ed Berry
The New World Atmosphere – Update
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Please see previous posting for links. This writing will be very short, and it is unlikely I will do one this weekend due to covering operational shifts and work to get the next weather-climate discussion out for posting on the ESRL/PSD MJO web site. I should be able to do a complete Blog discussion next Wednesday, 8/22. What I posted on August 12th is still quite valid.
Tropical Ocean SSTs remain above average across most of the Western Hemisphere and the Indian Ocean, with cooler than normal values centered on Indonesia. Actual SSTs in excess of 30C have been observed along and just north of the equator ~160E, with 29C and warmer over the TNWP as well as from the East Pacific, Caribbean into the Gulf of Mexico. Latest TAO data suggests the oceanic Kelvin wave is located around 160W, and that surface westerly wind anomalies (~5m/s) have once again returned to the equatorial date line region.
There continues to be little signal of a MJO, and there is some evidence of weak coupling between the tropical convection and warm SSTs west of the date line. An eastward propagating dynamical signal has emerged into the Western Hemisphere, moving along the East Pacific ITCZ as I type (phase speed ~8-10m/s). Finally, consolidation of tropical forcing is taking place centered ~10-15N/110E (including the monsoon systems), with an intense flare-up just north of the equator centered ~60E.
Consistent with previous events during the last several months, I would expect Indian Ocean flare-up to propagate northeast and also merge with the on-going convective activity from India to Southeast Asia. This whole region of enhancement could easily shift into the TNWP weeks 2-3 maintaining the tropical cyclone concern for that region.
While tropical convection should persist west of the date line (SST boundary forcing), general suppression may be the case around Indonesia, all during weeks 1 and 2. The TNWP forcing could easily reinvigorate the SST boundary forced convection west of the dateline afterwards. Finally, the Western Hemisphere dynamical signal may propagate though the Americas into the Atlantic by weeks 2-3, creating a tropical cyclone hazard for the East Pacific and perhaps the North Atlantic later on. The latter will need careful monitoring, especially for hybrids, particularly if the environment of the deep tropical Atlantic remains unfavorable.
Zonal mean westerly wind anomalies to continue to increase from 15S-25N, with magnitudes at 200mb ~5m/s at 15N. Animations of 150mb and 250mb daily mean vector wind anomalies shows the appearance of twin upper tropospheric anticyclones around the date line within the tropics, with distorted twin subtropical anticyclones ~120E. These anticyclones (with lower tropospheric cyclones – baroclinic processes) are the result of the divergent outflows from the tropical forcing discussed above. The pair at the date line is a response the SST boundary forcing (and perhaps an ENSO signal due to an evolving possible warm event; a slower process than subseasonal), and are contributing to the recent increase of zonal mean anomalous westerly flow throughout the tropical and subtropical atmospheres. I can link the large anticyclonic circulation anomaly just southeast of Greenland to at least once recent rapid Rossby wave energy dispersion (RWD) from the date line anticyclones forced by the SSTs. Some of the anomalous westerly flow is already impacting not only the Tropical North Atlantic, but even enhancing moisture transport into the Desert Southwest of the USA (interacting with the extratropics).
GSDM Stage 1-2 best describes the global circulation (see links to AAM plots). A transition to GSDM Stage 2 would be most probable during week 2, possibly persisting into week 3. Afterwards, offering anything statistically useful is unclear. This would suggest retrogression of the ridge back into the Great Basin and perhaps into Alaska, with a central and eastern North American trough. Responding to some of the initial conditions discussed above, most ensemble numerical models support this notion for week 2. However, uncertainty continues extremely high, and I have been suggesting this option for at least 2 weeks (which has not been a total bust). We have been dealing with an atmosphere having somewhat unusual forcing for at least the past few months, and trying to apply “conventional (linear) thinking” to it. For example, trying to apply MJO reasoning to dynamical processes that are not MJO. Expected weather has already been discussed in previous postings.
Ed Berry
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Please see previous posting for links. This writing will be very short, and it is unlikely I will do one this weekend due to covering operational shifts and work to get the next weather-climate discussion out for posting on the ESRL/PSD MJO web site. I should be able to do a complete Blog discussion next Wednesday, 8/22. What I posted on August 12th is still quite valid.
Tropical Ocean SSTs remain above average across most of the Western Hemisphere and the Indian Ocean, with cooler than normal values centered on Indonesia. Actual SSTs in excess of 30C have been observed along and just north of the equator ~160E, with 29C and warmer over the TNWP as well as from the East Pacific, Caribbean into the Gulf of Mexico. Latest TAO data suggests the oceanic Kelvin wave is located around 160W, and that surface westerly wind anomalies (~5m/s) have once again returned to the equatorial date line region.
There continues to be little signal of a MJO, and there is some evidence of weak coupling between the tropical convection and warm SSTs west of the date line. An eastward propagating dynamical signal has emerged into the Western Hemisphere, moving along the East Pacific ITCZ as I type (phase speed ~8-10m/s). Finally, consolidation of tropical forcing is taking place centered ~10-15N/110E (including the monsoon systems), with an intense flare-up just north of the equator centered ~60E.
Consistent with previous events during the last several months, I would expect Indian Ocean flare-up to propagate northeast and also merge with the on-going convective activity from India to Southeast Asia. This whole region of enhancement could easily shift into the TNWP weeks 2-3 maintaining the tropical cyclone concern for that region.
While tropical convection should persist west of the date line (SST boundary forcing), general suppression may be the case around Indonesia, all during weeks 1 and 2. The TNWP forcing could easily reinvigorate the SST boundary forced convection west of the dateline afterwards. Finally, the Western Hemisphere dynamical signal may propagate though the Americas into the Atlantic by weeks 2-3, creating a tropical cyclone hazard for the East Pacific and perhaps the North Atlantic later on. The latter will need careful monitoring, especially for hybrids, particularly if the environment of the deep tropical Atlantic remains unfavorable.
Zonal mean westerly wind anomalies to continue to increase from 15S-25N, with magnitudes at 200mb ~5m/s at 15N. Animations of 150mb and 250mb daily mean vector wind anomalies shows the appearance of twin upper tropospheric anticyclones around the date line within the tropics, with distorted twin subtropical anticyclones ~120E. These anticyclones (with lower tropospheric cyclones – baroclinic processes) are the result of the divergent outflows from the tropical forcing discussed above. The pair at the date line is a response the SST boundary forcing (and perhaps an ENSO signal due to an evolving possible warm event; a slower process than subseasonal), and are contributing to the recent increase of zonal mean anomalous westerly flow throughout the tropical and subtropical atmospheres. I can link the large anticyclonic circulation anomaly just southeast of Greenland to at least once recent rapid Rossby wave energy dispersion (RWD) from the date line anticyclones forced by the SSTs. Some of the anomalous westerly flow is already impacting not only the Tropical North Atlantic, but even enhancing moisture transport into the Desert Southwest of the USA (interacting with the extratropics).
GSDM Stage 1-2 best describes the global circulation (see links to AAM plots). A transition to GSDM Stage 2 would be most probable during week 2, possibly persisting into week 3. Afterwards, offering anything statistically useful is unclear. This would suggest retrogression of the ridge back into the Great Basin and perhaps into Alaska, with a central and eastern North American trough. Responding to some of the initial conditions discussed above, most ensemble numerical models support this notion for week 2. However, uncertainty continues extremely high, and I have been suggesting this option for at least 2 weeks (which has not been a total bust). We have been dealing with an atmosphere having somewhat unusual forcing for at least the past few months, and trying to apply “conventional (linear) thinking” to it. For example, trying to apply MJO reasoning to dynamical processes that are not MJO. Expected weather has already been discussed in previous postings.
Ed Berry
Saturday, August 12, 2006
The New World Atmosphere
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
There has been little change in the global tropical SSTs since my August 9th posting. Latest TAO data suggests the third (weak) downwelling oceanic Kelvin wave since mid-March was located around 165W based on the latest five-day averaged TAO data (link below). This feature was accompanied with SSTAs ~plus 1-2C down to about 100m.
The trades have increased across a good portion of the north tropical oceans during the last week, particularly across the Western Hemisphere. This includes the trade wind surge across the central and eastern equatorial Pacific. Surface easterly wind anomalies have been ~3 m/s, and have led to some reduction of the anomalous warmth across the central Pacific. There are still pockets of surface westerly wind anomalies from near the date line into Indonesia. In direct response to a recent consolidation of tropical convective forcing ~10-15N/120E, the Eastern Hemisphere monsoon systems have intensified (more said below). In fact, loosely surface cross-equatorial anomalous southerly flow generally exists from Africa to the date line, with magnitudes of ~5-10m/s. The recent (and expected) upsurge in tropical cyclone activity across the TNWP has contributed this cross-equatorial flow.
Additional global SST information can be obtained from latest TAO data here, ESRL/PSD data here, CPC data
http://www.cpc.ncep.noaa.gov/products/predictions/threats/index_gloss.html,
and BMRC at
http://www.bom.gov.au/bmrc/ocean/results/climocan.htm .
From continuous monitoring and various diagnostic and dynamical tools, there continues to be evidence that the weather-climate system is still tilting toward a warm event. The current trade wind surge discussed above has dampened some of the positive SSTAs associated with it. The following are links to recently updated and informative ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
To me, it is unclear what the magnitude of any possible warm event may be, including global impacts. I should also point out that the various modes of subseasonal variability (addressed in this Blog and part of the GSDM) which can initiate slower processes such as a warm event constantly impact the atmosphere in terms of forcing-circulation response and feedbacks. The latter includes extreme weather events.
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Details of consolidations and other behaviors of tropical forcing have been presented in previous writings and will not be repeated. Per 3-day OLRA plots, tropical forcing remains very intense from ~120E-170E at about 10-15N with magnitudes ~minus 50-90 W/m**2. Enhanced tropical convection is also spreading into the Western Hemisphere to about 150W, while the East Pacific ITCZ becomes more active. There is also another flare-up occurring along the equator in the western Indian Ocean (~40E), possibly related to dynamic forcing from the Southern Hemisphere. The latter is not the “first time” this has occurred during summer 2006. In fact, the latest 30-day OLRA plots show negative anomalies of ~15-25W/m**2 in this region (with suppression of ~plus 50-70 W/m**2 from the central equatorial Indian Ocean into Indonesia – see plots). These features have been propagating fairly rapidly north only to enhance the monsoon systems. What will this latest episode do???
I have not addressed a mode of tropical convective variability in these writings which may have been obvious to many others. Since roughly mid-late April 2006, there has been ~50-60 day enhancement of tropical convective forcing across the west central and TNWP, centered ~160E. After late April, there was enhancement during late June and also right now, with suppression during May and July. The weather-climate discussion we are working on will go into additional detail.
The AAM plots have shown a fairly clean atmospheric response signal to this ~50-60 day tropical convective mode. I should emphasize there are a whole spectrum of processes always going on in the atmosphere. The reasons why this ~50-60 day variability appeared are unclear to me. These may be a natural response to the many other faster dynamical processes I have been talking about in the presence little or no MJO and an emerging warm event. I do not know if these ~50-60 days modes are oscillatory, stationary, something purely stochastic, etc. Whatever the case, it is there and is a concern for attribution and prediction.
I can really make things even more “messy” by offering the tropical convective forcing we are now seeing coming into the Western Hemisphere may be our 30-day mode propagating east while the Indian Ocean flare-up may evolve into another convectively coupled Kelvin wave (and I am just getting started!). This is why disciplined monitoring every day is critical with the GSDM framework to have any hope of mitigating “weather surprises”. In the week 1-3 outlooks I will offer, I am going to focus of the ~50-60 day western Pacific tropical convective forcing signal. Even though my uncertainty will remain tremendously high, I do have slightly better confidence for weeks 1-3 than previously.
Please see http://www.npmoc.navy.mil/jtwc.html and http://www.nhc.noaa.gov/ for tropical cyclone concerns. Empirical, statistical and numerical prediction tools continue to be inconclusive for useful information about the future evolution of the tropical convection, and that is not going to change for the foreseeable future (bravely spoken!). Please see ESRL/PSD MJO tools , BMRC MJO tools, CPC MJO tools, and http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html for the details. These tools generally rely on a moderate to strong MJO signal, which is nearly non-existent at this time.
However, I think it is worthwhile to again note that the Wheeler index did have a ~1 sigma signal for about a couple of days last week, centered on Southeast Asia and the TNWP (see link), not inconsistent with the above and tropical wind fields (discussed below).
http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/RMM/phase.Last90days.gif.
There has not been much change to the distribution of 200mb zonal mean zonal wind anomalies since August 9th. There has been a slight increase in the magnitude of anomalous westerly flow ~ 15N with magnitudes ~5m/s (plots can be generated at http://www.cdc.noaa.gov/map/time_plot ; see for yourself some of the details).
If the reader generates a time-latitude section of 150mb zonal mean meridional wind anomalies since April 1st, 2006, a loose relationship between increased zonal mean divergence of ~3 m/s and enhanced convection across centered ~140E can been seen, following the ~50-60 time scale. Of course, this enhanced divergence will shift northward with the seasonal cycle, and may suggest a local increase in the Hadley Cell. The latter may be true at this time.
Global AAM signals are relatively weak, and links are given to the plots. However, I want to make the point that the global frictional torque is already at ~plus 10 Hadleys above the 1968-1997 reanalysis climatology as of August 9th, with a large contribution from the above normal trades. I think we are going to see behaviors similar to roughly April into early May and mid-late June into early July meaning another strong positive phase of a global (remember) mountain-frictional torque index cycle linked to the ~50-60 day tropical convective mode. Recall that the global frictional torque leads the mountain torque by ~6 days.
Animations of 150mb and 250mb daily mean vector wind anomalies still depict loose twin subtropical anticyclones centered around 120-140E in a region of anomalous divergence. Westerly wind anomalies ~15-25m/s continue to be present throughout much of the tropical Pacific into Northern South America, while anomalous easterly flow slowly collapses from the Indian Ocean into Africa. I might also mention that I can link the recent appearance of the large anticyclonic circulation gyre just southeast of Greenland to a recent fast Rossby wave energy dispersion (RWD) initiated by our 30-day convective mode (is that what it is?) crossing the date line into the Western Hemisphere.
To summarize, I think we have a weather-climate situation consisting of 1) the ~50-60 day tropical convective mode, 2) the ~30-day convective mode, 3) other faster modes of tropical convective variability like those caused by the Southern Hemisphere which are nothing but noise, 4) the ~50-day mountain-frictional torque index cycle going perhaps into a positive phase, 5) the rapid extratropical Rossby wave energy dispersions/baroclinic wave packets, 6) weak or non-existent MJO, which may be part of a “new world atmosphere” emerging (I need to add some “strange humor”), 7) possible ENSO and/or global warming signal, and 8) seasonal transition into boreal autumn. The latter includes the strengthening Northern Hemisphere polar vortex, which should displace toward the TNWP convective forcing initially. Restating, I can list a lot of components within our GSDM framework; however, it still all adds up to a weak predictive signal at best.
GSDM Stage 1-2 best describes the current global circulation/weather-climate situation. My thoughts are about another week or so of this situation, with an evolution to GSDM Stage 2 weeks 2-3. Understanding seasonal transition, if there is any truth to our ~50-60 day mode remaining coherent, weeks 3-4 may see a transition to GSDM Stage 3-4, possible evolving to GSDM 4-1 weeks 4-6. Of course, this timing is not statistically useful (noise), but is offered out of concern for the North Atlantic hurricane season. From the subseasonal viewpoint, a scenario of conditions becoming favorable for North Atlantic tropical cyclogenesis as the climatological peak approaches must be monitored.
Week 1 (13-19 August 2006): GSDM Stage 1-2 seems probable. Per the NCEP GFS and other models, there look to be at least 1 or 2 more mobile troughs to dig along the USA west coast, then move inland through the northern states. This would suggest additional episodes of heat to expand from the Central Rockies into much of the Central/Southern Plains and Deep South. An active severe local storm/MCS track would be possible from the Northern/Central Rockies into the Mid/Upper Mississippi Valley/Great Lakes-Ohio Valley. While tropical cyclogenesis may become active across the East Pacific while the TNWP remains quite active, the Atlantic should remain suppressed.
Week 2 (20-26 August 2006): Transition to GSDM 2 would be expected, which means synoptically I may finally see the ridge shift back into the western USA. A downstream central and eastern states trough would be expected. Many models responding to initial conditions are supportive. The anticyclone developing just south of Greenland could shift toward the west, and may contribute an extended period of a negative NAO (I can talk indices too!). The NAO is already negative linked to the flare-up discussed above. While the western states warms/dries, the central and east would be expected to become cooler and wetter. Tropical cyclone development across the North Atlantic may remain suppressed while the East Pacific may be active.
Week 3 (27 August – 2 September 2006): GSDM Stage 2 may mature, perhaps transitioning to GSDM Stage 3. Synoptically this could be a period similar to late June (West Coast ridge maybe into AK, Mississippi Valley/Plains trough, etc.) understanding the seasonal cycle, with the expected weather.
I hope Southwest Kansas can get some much needed rainfall week 1. Timing of fronts with the diurnal cycle of thunderstorm activity has been just one of many factors not favorable for rainfall this summer. I can see this same scenario for portions of this area on Sunday, August 13th. Hopefully the dynamics with the mobile troughs will mitigate some of that. Weeks 2-3 are unclear given our climate sensitivity, especially if the ridge retrogrades. Broadly I would expect a dry regime as the ridge shifts back toward the West Coast while temperatures remain near-above average. At some point a decent surge of cooler than normal air may be possible as Labor Day approaches. To improve our rain chances we need the westerlies farther south with a trough position across the central Rockies (there are other favorable patterns).
The time -filtered coherent modes Hovmoller plots of OLR and OLRA are at http://www.cdc.noaa.gov/map/clim/olr_modes/), velocity potential Hovmollers at http://www.cpc.ncep.noaa.gov/products/intraseasonal/vpot_tlon.html , and an animation of velocity potential overlayed on OLRAs are at http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ir_anim_monthly.shtml.
Satellite imagery and other information can be found from the following links: eastern hemisphere, full-disk west Pacific, mtsat, IO, Africa, http://www.jma.go.jp/en/gms/ ; other imagery here. Latest tropical cyclone statements can be found from http://www.nhc.noaa.gov/, while the latest 3-day averages of OLR totals and anomalies and other data can be found here
http://www.cdc.noaa.gov/map/clim/glbcir.anim.shtml (animations of various fields from the operational data)
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml (Global Tropical Hazards Assessment available from this site, along with other useful information)
http://www.cdc.noaa.gov/map/clim/aam.rean.shtml (reanalysis AAM plots)
http://www.cdc.noaa.gov/map/clim/aam.shtml (operational AAM plots)
Latest CDC Ensemble Forecast
Latest NCEP Ensemble Forecast
Additional NCEP Ensemble Output
Latest Canadian Ensemble Output
Latest Deterministic ECMWF Forecasts
http://www.cdc.noaa.gov/people/jeffrey.s.whitaker/refcst/week2/
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html (link to our Weather-
Climate discussions)
http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html (model performance; please navigate to others)
Please see the CPC Drought Monitor for areas of dryness and the latest official outlooks and statements from the Storm Prediction Center not only for severe storms, but also fire weather concerns. Finally, the CPC USA Hazards Assessment for offers additional insights not only for possible week 1 high impact weather, but week 2 as well.
I will try to do another posting around Tuesday, next week. Work is also on-going to post a weather-climate discussion on the ESRL/PSD MJO web site hopefully by about the middle of this month. Due to shift work obligations (graveyards), my next couple of postings may be quite brief, with the possibility of missing next weekend.
Ed Berry
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions (link at the bottom) with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
There has been little change in the global tropical SSTs since my August 9th posting. Latest TAO data suggests the third (weak) downwelling oceanic Kelvin wave since mid-March was located around 165W based on the latest five-day averaged TAO data (link below). This feature was accompanied with SSTAs ~plus 1-2C down to about 100m.
The trades have increased across a good portion of the north tropical oceans during the last week, particularly across the Western Hemisphere. This includes the trade wind surge across the central and eastern equatorial Pacific. Surface easterly wind anomalies have been ~3 m/s, and have led to some reduction of the anomalous warmth across the central Pacific. There are still pockets of surface westerly wind anomalies from near the date line into Indonesia. In direct response to a recent consolidation of tropical convective forcing ~10-15N/120E, the Eastern Hemisphere monsoon systems have intensified (more said below). In fact, loosely surface cross-equatorial anomalous southerly flow generally exists from Africa to the date line, with magnitudes of ~5-10m/s. The recent (and expected) upsurge in tropical cyclone activity across the TNWP has contributed this cross-equatorial flow.
Additional global SST information can be obtained from latest TAO data here, ESRL/PSD data here, CPC data
http://www.cpc.ncep.noaa.gov/products/predictions/threats/index_gloss.html,
and BMRC at
http://www.bom.gov.au/bmrc/ocean/results/climocan.htm .
From continuous monitoring and various diagnostic and dynamical tools, there continues to be evidence that the weather-climate system is still tilting toward a warm event. The current trade wind surge discussed above has dampened some of the positive SSTAs associated with it. The following are links to recently updated and informative ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
To me, it is unclear what the magnitude of any possible warm event may be, including global impacts. I should also point out that the various modes of subseasonal variability (addressed in this Blog and part of the GSDM) which can initiate slower processes such as a warm event constantly impact the atmosphere in terms of forcing-circulation response and feedbacks. The latter includes extreme weather events.
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Details of consolidations and other behaviors of tropical forcing have been presented in previous writings and will not be repeated. Per 3-day OLRA plots, tropical forcing remains very intense from ~120E-170E at about 10-15N with magnitudes ~minus 50-90 W/m**2. Enhanced tropical convection is also spreading into the Western Hemisphere to about 150W, while the East Pacific ITCZ becomes more active. There is also another flare-up occurring along the equator in the western Indian Ocean (~40E), possibly related to dynamic forcing from the Southern Hemisphere. The latter is not the “first time” this has occurred during summer 2006. In fact, the latest 30-day OLRA plots show negative anomalies of ~15-25W/m**2 in this region (with suppression of ~plus 50-70 W/m**2 from the central equatorial Indian Ocean into Indonesia – see plots). These features have been propagating fairly rapidly north only to enhance the monsoon systems. What will this latest episode do???
I have not addressed a mode of tropical convective variability in these writings which may have been obvious to many others. Since roughly mid-late April 2006, there has been ~50-60 day enhancement of tropical convective forcing across the west central and TNWP, centered ~160E. After late April, there was enhancement during late June and also right now, with suppression during May and July. The weather-climate discussion we are working on will go into additional detail.
The AAM plots have shown a fairly clean atmospheric response signal to this ~50-60 day tropical convective mode. I should emphasize there are a whole spectrum of processes always going on in the atmosphere. The reasons why this ~50-60 day variability appeared are unclear to me. These may be a natural response to the many other faster dynamical processes I have been talking about in the presence little or no MJO and an emerging warm event. I do not know if these ~50-60 days modes are oscillatory, stationary, something purely stochastic, etc. Whatever the case, it is there and is a concern for attribution and prediction.
I can really make things even more “messy” by offering the tropical convective forcing we are now seeing coming into the Western Hemisphere may be our 30-day mode propagating east while the Indian Ocean flare-up may evolve into another convectively coupled Kelvin wave (and I am just getting started!). This is why disciplined monitoring every day is critical with the GSDM framework to have any hope of mitigating “weather surprises”. In the week 1-3 outlooks I will offer, I am going to focus of the ~50-60 day western Pacific tropical convective forcing signal. Even though my uncertainty will remain tremendously high, I do have slightly better confidence for weeks 1-3 than previously.
Please see http://www.npmoc.navy.mil/jtwc.html and http://www.nhc.noaa.gov/ for tropical cyclone concerns. Empirical, statistical and numerical prediction tools continue to be inconclusive for useful information about the future evolution of the tropical convection, and that is not going to change for the foreseeable future (bravely spoken!). Please see ESRL/PSD MJO tools , BMRC MJO tools, CPC MJO tools, and http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html for the details. These tools generally rely on a moderate to strong MJO signal, which is nearly non-existent at this time.
However, I think it is worthwhile to again note that the Wheeler index did have a ~1 sigma signal for about a couple of days last week, centered on Southeast Asia and the TNWP (see link), not inconsistent with the above and tropical wind fields (discussed below).
http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/RMM/phase.Last90days.gif.
There has not been much change to the distribution of 200mb zonal mean zonal wind anomalies since August 9th. There has been a slight increase in the magnitude of anomalous westerly flow ~ 15N with magnitudes ~5m/s (plots can be generated at http://www.cdc.noaa.gov/map/time_plot ; see for yourself some of the details).
If the reader generates a time-latitude section of 150mb zonal mean meridional wind anomalies since April 1st, 2006, a loose relationship between increased zonal mean divergence of ~3 m/s and enhanced convection across centered ~140E can been seen, following the ~50-60 time scale. Of course, this enhanced divergence will shift northward with the seasonal cycle, and may suggest a local increase in the Hadley Cell. The latter may be true at this time.
Global AAM signals are relatively weak, and links are given to the plots. However, I want to make the point that the global frictional torque is already at ~plus 10 Hadleys above the 1968-1997 reanalysis climatology as of August 9th, with a large contribution from the above normal trades. I think we are going to see behaviors similar to roughly April into early May and mid-late June into early July meaning another strong positive phase of a global (remember) mountain-frictional torque index cycle linked to the ~50-60 day tropical convective mode. Recall that the global frictional torque leads the mountain torque by ~6 days.
Animations of 150mb and 250mb daily mean vector wind anomalies still depict loose twin subtropical anticyclones centered around 120-140E in a region of anomalous divergence. Westerly wind anomalies ~15-25m/s continue to be present throughout much of the tropical Pacific into Northern South America, while anomalous easterly flow slowly collapses from the Indian Ocean into Africa. I might also mention that I can link the recent appearance of the large anticyclonic circulation gyre just southeast of Greenland to a recent fast Rossby wave energy dispersion (RWD) initiated by our 30-day convective mode (is that what it is?) crossing the date line into the Western Hemisphere.
To summarize, I think we have a weather-climate situation consisting of 1) the ~50-60 day tropical convective mode, 2) the ~30-day convective mode, 3) other faster modes of tropical convective variability like those caused by the Southern Hemisphere which are nothing but noise, 4) the ~50-day mountain-frictional torque index cycle going perhaps into a positive phase, 5) the rapid extratropical Rossby wave energy dispersions/baroclinic wave packets, 6) weak or non-existent MJO, which may be part of a “new world atmosphere” emerging (I need to add some “strange humor”), 7) possible ENSO and/or global warming signal, and 8) seasonal transition into boreal autumn. The latter includes the strengthening Northern Hemisphere polar vortex, which should displace toward the TNWP convective forcing initially. Restating, I can list a lot of components within our GSDM framework; however, it still all adds up to a weak predictive signal at best.
GSDM Stage 1-2 best describes the current global circulation/weather-climate situation. My thoughts are about another week or so of this situation, with an evolution to GSDM Stage 2 weeks 2-3. Understanding seasonal transition, if there is any truth to our ~50-60 day mode remaining coherent, weeks 3-4 may see a transition to GSDM Stage 3-4, possible evolving to GSDM 4-1 weeks 4-6. Of course, this timing is not statistically useful (noise), but is offered out of concern for the North Atlantic hurricane season. From the subseasonal viewpoint, a scenario of conditions becoming favorable for North Atlantic tropical cyclogenesis as the climatological peak approaches must be monitored.
Week 1 (13-19 August 2006): GSDM Stage 1-2 seems probable. Per the NCEP GFS and other models, there look to be at least 1 or 2 more mobile troughs to dig along the USA west coast, then move inland through the northern states. This would suggest additional episodes of heat to expand from the Central Rockies into much of the Central/Southern Plains and Deep South. An active severe local storm/MCS track would be possible from the Northern/Central Rockies into the Mid/Upper Mississippi Valley/Great Lakes-Ohio Valley. While tropical cyclogenesis may become active across the East Pacific while the TNWP remains quite active, the Atlantic should remain suppressed.
Week 2 (20-26 August 2006): Transition to GSDM 2 would be expected, which means synoptically I may finally see the ridge shift back into the western USA. A downstream central and eastern states trough would be expected. Many models responding to initial conditions are supportive. The anticyclone developing just south of Greenland could shift toward the west, and may contribute an extended period of a negative NAO (I can talk indices too!). The NAO is already negative linked to the flare-up discussed above. While the western states warms/dries, the central and east would be expected to become cooler and wetter. Tropical cyclone development across the North Atlantic may remain suppressed while the East Pacific may be active.
Week 3 (27 August – 2 September 2006): GSDM Stage 2 may mature, perhaps transitioning to GSDM Stage 3. Synoptically this could be a period similar to late June (West Coast ridge maybe into AK, Mississippi Valley/Plains trough, etc.) understanding the seasonal cycle, with the expected weather.
I hope Southwest Kansas can get some much needed rainfall week 1. Timing of fronts with the diurnal cycle of thunderstorm activity has been just one of many factors not favorable for rainfall this summer. I can see this same scenario for portions of this area on Sunday, August 13th. Hopefully the dynamics with the mobile troughs will mitigate some of that. Weeks 2-3 are unclear given our climate sensitivity, especially if the ridge retrogrades. Broadly I would expect a dry regime as the ridge shifts back toward the West Coast while temperatures remain near-above average. At some point a decent surge of cooler than normal air may be possible as Labor Day approaches. To improve our rain chances we need the westerlies farther south with a trough position across the central Rockies (there are other favorable patterns).
The time -filtered coherent modes Hovmoller plots of OLR and OLRA are at http://www.cdc.noaa.gov/map/clim/olr_modes/), velocity potential Hovmollers at http://www.cpc.ncep.noaa.gov/products/intraseasonal/vpot_tlon.html , and an animation of velocity potential overlayed on OLRAs are at http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ir_anim_monthly.shtml.
Satellite imagery and other information can be found from the following links: eastern hemisphere, full-disk west Pacific, mtsat, IO, Africa, http://www.jma.go.jp/en/gms/ ; other imagery here. Latest tropical cyclone statements can be found from http://www.nhc.noaa.gov/, while the latest 3-day averages of OLR totals and anomalies and other data can be found here
http://www.cdc.noaa.gov/map/clim/glbcir.anim.shtml (animations of various fields from the operational data)
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml (Global Tropical Hazards Assessment available from this site, along with other useful information)
http://www.cdc.noaa.gov/map/clim/aam.rean.shtml (reanalysis AAM plots)
http://www.cdc.noaa.gov/map/clim/aam.shtml (operational AAM plots)
Latest CDC Ensemble Forecast
Latest NCEP Ensemble Forecast
Additional NCEP Ensemble Output
Latest Canadian Ensemble Output
Latest Deterministic ECMWF Forecasts
http://www.cdc.noaa.gov/people/jeffrey.s.whitaker/refcst/week2/
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html (link to our Weather-
Climate discussions)
http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html (model performance; please navigate to others)
Please see the CPC Drought Monitor for areas of dryness and the latest official outlooks and statements from the Storm Prediction Center not only for severe storms, but also fire weather concerns. Finally, the CPC USA Hazards Assessment for offers additional insights not only for possible week 1 high impact weather, but week 2 as well.
I will try to do another posting around Tuesday, next week. Work is also on-going to post a weather-climate discussion on the ESRL/PSD MJO web site hopefully by about the middle of this month. Due to shift work obligations (graveyards), my next couple of postings may be quite brief, with the possibility of missing next weekend.
Ed Berry
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