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

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

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

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

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