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 SST anomalies still resembles a mature warm event, with positive values across the western Indian Ocean and along the equator from ~170E-South America and cool readings around Indonesia particularly south of the equator. Magnitudes as low as ~minus 2C and lower were observed north of Australia on 26 October while ~plus 2C just east of the equatorial date line and west of South America (keep in mind the seasonal cycle of SSTs). The SST horse shoe pattern of cool surrounding warm anomalies (would be reversed for a cold event) across the tropical Indo-Pacific remains, and is best defined across the Southern Hemisphere with values ~minus 1-2C.
SSTs of 30C and warmer cover much of the equatorial date line region while ~29-29.5C waters are present across the central Indian Ocean and around both sides of Central America. Weak positive SST anomalies cover most of the tropical Atlantic with actual temperatures ~28-29C.
There is some evidence that the warm-cool-warm SSTs discussed above have shifted ~10 degrees east during the last week or so. The recent surface westerly wind event (WWE) with anomalies in excess of 10m/s (westerly anomalies still remain along and east of the date line) has apparently excited another oceanic Kelvin wave which is propagating toward the east Pacific. Anomalies as high as plus 4C down ~150m at 170W were observed per recent TAO array buoy data. This oceanic Kelvin wave along with an advective component from the anomalous westerly flow may be helping to shift the SST distribution to the east.
The WWE tied to the recent MJO helped to strengthen our warm ENSO. At this point I see 2 ocean basins with warm SSTs, the central equatorial Indian Ocean and the date line. There are folks that will call the former a positive phase of the Indian Ocean Dipole (IOD) and others which feel this SST distribution is consistent with a warm event (I feel the latter). Whatever the case, I try to understand the weather-climate situation from a dynamical forcing-response-feedback perspective, and I think I can see physically how this whole SST situation evolved starting around March 2006 (too long to discuss here). The point is both of these warm ocean basins (and other oceanic regions) are currently impacting the circulation and will continue to do so.
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/
Full disk satellite imagery and other monitoring tools (coherent modes Hovmollers, velocity potential/OLRA animations, etc.) suggest the dynamical signal with the MJO has returned to the Eastern Hemisphere and was located ~60E. The phase speed of this signal has slowed considerably and its magnitude has significantly weakened. Tropical convective forcing has been increasing across much of the central Indian Ocean and in a band from the South Pacific toward the Philippines (with Tropical Cyclone Cimaron). Enhanced convection has recently been propagating east-southeast along the South Pacific Convergence Zone (SPCZ) (weakly projecting onto a convectively coupled Kelvin wave) while also shifting back toward the Philippines. In fact, the recent pattern of Indian Ocean enhancement-Indonesian suppression- west Pacific enhancement is less robust than a week ago.
My own thought is we may see some consolidation of the tropical convective forcing ~ 10-15N/90-120E during the next 1-2 weeks (north of the cool SSTs). However, flare-ups across both the Indian Ocean and especially the date line/South Pacific region may occur “any time”. Illustrations of this kind of behavior are the weather-climate events during past 4 weeks or so which we hope to detail in another weather-climate discussion for the ESRL/PSD MJO web page.
Briefly, as the dynamical signal with the MJO interacted with the warm date line SSTs during late September and early October, a Rossby wave energy dispersion (RWD) occurred across the PNA sector leading to a deep trough across the Great Lakes and North Atlantic blocking by around 12-14 October (recall the Buffalo, NY snow event). There were subsequent RWDs from the North Atlantic blocking which interacted with other wave packets moving across Asia. These helped to re-invigorate the date line tropical convection through their enhanced divergent upper tropospheric outflows all while the MJO signal was moving through the Western Hemisphere, by about 15 October. Among other responses, there was a central/east tropical Pacific basin wide surface westerly wind event with anomalies well in excess of 10m/s which helped to strengthen the warm ENSO. To me, this is a situation of tropics forcing extratropics (including from the MJO and ENSO in this case) and then extratropics forcing back (with properly phased wave trains) to maintain an “equilibrium weather-climate situation” through the interactions of multiple time scales.
A “repeat” of the above recently occurred about 5 days ago with another flare-up of date line tropical forcing (~every 20 days for a time-scale?) which led to intense baroclinic storm development from the central/southern Rockies to the eastern part of the USA. A difference is the MJO signal had re-emerged into the Eastern Hemisphere (and weakened). The models did struggle with the synoptic details of this storm (which was responsible for a blizzard across eastern Colorado and possibly more than 2 dozen tornadoes across Southwest Kansas).
Is the recent intensification of the Indian Ocean convection going to “disrupt this feedback loop?” Has this latest MJO caused our warm event to (finally) peak? Are we going to see 2 (or more) regions of tropical forcing with the Indian Ocean convection (eventually spreading east inconsideration of the SSTs?) becoming dominate at some point? Will there be another coherent MJO signal? These are just some of the issues that are unclear.
Evidence of circulation impacts from the variability of the date line tropical forcing can also be seen from plots of the earth-atmosphere AAM budget available from ESRL/PSD (using the re-analysis data and its 1968-97 climatology). Loosely, around 1 October global relative AAM tendency was positive with positive global mountain and frictional torques. That all reversed by about the middle of this month only to recently become positive (magnitudes ~10-20 Hadleys). Global relative AAM has lagged by roughly 10 days.
There has also been poleward propagation of zonal mean westerly wind anomalies into both the midlatitude and subtropical atmospheres of the Northern Hemispheres with anomalies ~5-10m/s at 200mb linked to the tropical forcing. Animations of both 150mb and 250mb daily mean vector wind anomalies show the presence of anomalous twin subtropical anticyclones across the Western Hemisphere coming back into the Indian Ocean while a separate pair persists near the date line. The former have been associated with the MJO signal while the latter is at least partly from ENSO. There is a well defined subtropical jet (STJ) extending from the date line pair (as also seen from full-disk satellite water vapor imagery) with additional enhancement from the anticyclones downstream. Anomalies with this STJ have been in excess of 25 m/s at 150mb at times.
Overall we have a weather-climate situation I would offer is best described by GSDM Stage 4 but with additional complexity due to the date line tropical forcing. I have been terming the latter as a signal due to the current warm phase of ENSO throughout this discussion. However, in reality I think there may be even slower time scales involved with this along with “other processes”, in addition to ENSO.
To summarize, I think we have 1) a warm event (plus a global warming signal whose cause is unclear?), 2) possibly an increasing role of the Indian Ocean SSTs, 3) the MJO signal which may become very weak, 4) 20-30 day tropical convective variability, 5) some evidence of mountain-frictional torque index cycle variations (not discussed – may be linked to (4)), fast RWDs, baroclinic wave packets and all sorts of other white noise, and 6) seasonal cycle issues.
The latter (6) may involve just how sensitive the response across the Asia-PNA sector will become to tropical convective forcing (or lack of) as the climatological strengthening of the East Asian Jet (EAJ) occurs. For instance, if we do get into a situation of 2 regions of tropical forcing (with suppression, say around the Philippines), the response may become GSDM Stage 1 with STJs through late December. Afterwards, as both the convection and EAJ shift south, enhanced convection across the central Pacific may become dominate and lead to GSDM Stage 3 by sometime in January. We will see.
In what follows, I am leaning toward my notion of consolidation of the tropical forcing during weeks 1-2 per above. Afterwards, I think it is unclear to offer anything statistically useful without additional tools. Confidence remains as low as it can ever get making week 1-3 predictions in this weather-climate situation. This is why detailed disciplined daily monitoring is critical.
Week 1 (28 October – 3 November 2006): GSDM Stage 4 with additional forcing from the central Pacific appears probable. The models are generally consistent with mid/upper tropospheric trough development across the east Pacific (~140W) with a downstream ridge along the west coast and subsequent eastern states trough by early next week. I see no reason to differ given the central Pacific twin subtropical anticyclones. At some point I would expect the westerly flow to increase across East Asia as trough development occurs there. This should allow the east Pacific trough to approach the west coast going into week 2.
This situation is generally dry for most of the country with warm conditions across the western states and cool for the east (not all the unusual for this time of year). The Pacific Northwest should have increasing opportunities for rainfall. There may also be opportunities for rainfall across the Deep South at times tied to the STJ.
Week 2 (4-10 November 2006): GSDM Stage 1 with an above average STJ may be most probable. At this point particularly the Pacific Northwest may receive substantial precipitation, which could spread slowly south. Depending on how far inland the trough gets, cooler and wetter weather may become more likely for the portions of the Rockies. The rest of the country may see above normal temperatures.
Week 3 (11-17November 2006): Unclear; however, an eastward progression of the situation discussed for week 2 would be reasonable if there is any truth to it.
Climatologically this is still the dry time of the year for Southwest Kansas. The recent storm/rain event was a pleasant “surprise (other than the tornadoes depending on your perspective)”. Week 1 looks generally dry with near-below normal temperatures (on average). Dryness may continue well into week 2 while temperatures may warm to well above average. Jet streaks along the STJ could give us at least a minor precipitation surprise by then. An active regime may return for this part of the world week 3 (for this time of year).
I will be on travel to ESRL/PSD next week so I do not know when there will be another posting on this Blog (perhaps a short one ~ middle of next week). We do have plans to write another weather-climate discussion for the ESRL/PSD MJO web page to hopefully post by the end of November. 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 27, 2006
Sunday, October 22, 2006
Update on What Goes Around Gets Messy -- written 10/21/06
This posting will be very brief. I hope to do a more complete effort late this upcoming week after I have completed covering overnight shifts (~10/26-27/06). Please see other postings for all web links.
The spatial distribution of global tropical SSTs are consistent with a mature warm ENSO. Strong westerly wind anomalies (~10m/s) and actual westerlies remain across the equatorial date line region. In fact, TAO buoy data suggest a downwelling oceanic Kelvin wave has developed east of the date line and is moving east along the equatorial cold tongue. We will see how robust this warm event gets (there is always uncertainty in many different aspects). At this point odds would favor above normal surface temperatures for especially the north central states during DJF and JFM (see CPC outlooks). However, please remember these are seasonal mean indications and this does not at all rule out possibilities of extreme cold episodes along with other forms of high impact severe winter weather for the northern or any portions of the USA.
The dynamical signal with the MJO is moving into the Eastern Hemisphere while SST boundary forced tropical convection slowly increases across the central Indian Ocean and west Pacific (per full disk satellite imagery). Three-day mean charts of OLRA indicate enhanced rainfall is present just south of the equator ~60E, 160E-160W including the SPCZ and from much of northern South America into the Atlantic ITCZ. Anomalous upper tropospheric twin tropical/subtropical anticyclones (with lower level westerly anomalies – baroclinic response) accompany these 3 regions, particularly for the MJO dynamical signal.
Re-analysis data plots from ESRL/PSD shows global relative AAM tendency has become strongly negative (as of 10/18) with a magnitude of ~ minus 25 Hadleys. Both the global mountain and frictional torques are contributing. Zonal mean easterly wind anomalies are replacing westerly anomalies throughout the tropical and subtropical atmospheres while existing westerly anomalies propagate into the midlatitudes of both hemispheres. In this type of situation a synoptician is going to see a tendency for troughs and ridges to become northeast-southwest oriented across the Northern Hemisphere along with features such as anticyclonically wave breaking (AWB) “upper level lows”. These tilts will contribute to AAM being fluxed poleward from the tropics into eventually the midlatitudes.
GSDM Stage 4 best describes the current weather-climate situation. The future evolution of the tropical convective forcing is unclear, including if there will be another MJO. My own thought is we may see some consolidation of the tropical forcing across the Eastern Hemisphere during the next 1-3 weeks, perhaps around 10N/90-120E to the north of the cool Indonesian SSTs. While this may be occurring, the date line region and even the SPCZ may continue experience tropical convective flare-ups (there are still the ~20-30 day tropical convective variability and convectively coupled Kelvin waves going on). Locations such as the South Indian Ocean-Bay of Bengal and west central and South Pacific may be vulnerable to tropical cyclone development (and we need to watch the Caribbean and even the North Atlantic for especially hybrids). During weeks 2-3 GSDM Stage 1 with subtropical jets may be most probable particularly for the Asia-PNA sector. This would suggest western North America to become increasingly at risk to strong synoptic-scale troughs while an active storm track develops across the Plains possibly going well into November. Most readers should be familiar what all this means in terms of weather particularly if a cold air source evolves during November.
Ed Berry
The spatial distribution of global tropical SSTs are consistent with a mature warm ENSO. Strong westerly wind anomalies (~10m/s) and actual westerlies remain across the equatorial date line region. In fact, TAO buoy data suggest a downwelling oceanic Kelvin wave has developed east of the date line and is moving east along the equatorial cold tongue. We will see how robust this warm event gets (there is always uncertainty in many different aspects). At this point odds would favor above normal surface temperatures for especially the north central states during DJF and JFM (see CPC outlooks). However, please remember these are seasonal mean indications and this does not at all rule out possibilities of extreme cold episodes along with other forms of high impact severe winter weather for the northern or any portions of the USA.
The dynamical signal with the MJO is moving into the Eastern Hemisphere while SST boundary forced tropical convection slowly increases across the central Indian Ocean and west Pacific (per full disk satellite imagery). Three-day mean charts of OLRA indicate enhanced rainfall is present just south of the equator ~60E, 160E-160W including the SPCZ and from much of northern South America into the Atlantic ITCZ. Anomalous upper tropospheric twin tropical/subtropical anticyclones (with lower level westerly anomalies – baroclinic response) accompany these 3 regions, particularly for the MJO dynamical signal.
Re-analysis data plots from ESRL/PSD shows global relative AAM tendency has become strongly negative (as of 10/18) with a magnitude of ~ minus 25 Hadleys. Both the global mountain and frictional torques are contributing. Zonal mean easterly wind anomalies are replacing westerly anomalies throughout the tropical and subtropical atmospheres while existing westerly anomalies propagate into the midlatitudes of both hemispheres. In this type of situation a synoptician is going to see a tendency for troughs and ridges to become northeast-southwest oriented across the Northern Hemisphere along with features such as anticyclonically wave breaking (AWB) “upper level lows”. These tilts will contribute to AAM being fluxed poleward from the tropics into eventually the midlatitudes.
GSDM Stage 4 best describes the current weather-climate situation. The future evolution of the tropical convective forcing is unclear, including if there will be another MJO. My own thought is we may see some consolidation of the tropical forcing across the Eastern Hemisphere during the next 1-3 weeks, perhaps around 10N/90-120E to the north of the cool Indonesian SSTs. While this may be occurring, the date line region and even the SPCZ may continue experience tropical convective flare-ups (there are still the ~20-30 day tropical convective variability and convectively coupled Kelvin waves going on). Locations such as the South Indian Ocean-Bay of Bengal and west central and South Pacific may be vulnerable to tropical cyclone development (and we need to watch the Caribbean and even the North Atlantic for especially hybrids). During weeks 2-3 GSDM Stage 1 with subtropical jets may be most probable particularly for the Asia-PNA sector. This would suggest western North America to become increasingly at risk to strong synoptic-scale troughs while an active storm track develops across the Plains possibly going well into November. Most readers should be familiar what all this means in terms of weather particularly if a cold air source evolves during November.
Ed Berry
Tuesday, October 17, 2006
ENSO and Complexity Making a Comeback
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 SST anomalies continues to resemble a mature warm event, with positive values across the western Indian Ocean and along the equator from ~140E-South America with cool readings around Indonesia particularly south of the equator. In fact, the SST horse shoe pattern of cool surrounding warm anomalies (would be reversed for a cold event) across the tropical Indo-Pacific is quite well defined. Anomalies are generally from 1-2C with magnitudes around 3C along the East Pacific cold tongue, extending to depths of ~200m around the date line. SSTs of 29C and warmer cover much of the equatorial date line region, the central Indian Ocean and both sides of Central America. Weak positive SST anomalies cover most of the tropical Atlantic with actual temperatures ~28-29C.
SST and SST anomaly tendencies during the past week or so have reinforced the spatial distribution discussed above. Magnitudes have been ~plus .5-1C, with the warming along the equatorial cold tongue the result of a basin-wide surface westerly wind event whose anomalies have exceeded 10m/s (more said below). At this point our warm event has become better defined during the past 1-2 weeks. I have expressed concern in past writings this event may have already peaked. Whether or not this is the case, is unclear to me, as is the future for this warm ENSO (there are seasonal cycle issues). Whatever the case, the SSTs linked to this ENSO evolution have already impacted synoptic variability across North America since at least June 2006, and are doing so as I type.
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/
Per coherent modes and velocity potential Hovmollers (and other monitoring tools), the dynamical signal with the MJO is in the Western Hemisphere ~0/60W having a phase speed of ~10-15m/s. The MJO signal typically propagates eastward much faster across the Western Hemisphere due to less air/sea coupling with cooler SSTs (loosely acting like a Kelvin wave enhancing upper tropospheric divergence). Full disk satellite imagery shows quite a bit of convective enhancement centered on northern South America with OLRAs ~minus 50-90W/m**2. The recent heavy rainfall across the USA Deep South had a contribution from this MJO signal as the result of a local enhancement of the subtropical jet (STJ) via complex interactions with the extratropics.
Well defined twin upper tropospheric subtropical anticyclones are present around 90-120W (including the Gulf of Mexico) with wind speed anomalies ~20-30m/s per animations of 150mb daily mean vector wind anomalies. Additionally, Rossby wave energy is dispersing into the extratropics of both hemispheres leading to, for example, a negative projection onto the North Atlantic Oscillation (NAO).
Full disk satellite imagery also shows tropical convection increasing across the west central Pacific centered ~0/150-160E as well as the equatorial Indian Ocean ~60E, while strong suppression remains across Indonesia with positive values of OLRA in excess of 70 W/m**2 ~0/100E. This spatial pattern of enhancement-suppression-enhancement across the Eastern Hemisphere would be expected from the SSTs, with the former termed by some folks as a positive phase of the Indian Ocean Dipole (IOD) and the latter due to ENSO. It is typical to see a warm western Indian Ocean during a mature warm ENSO, and I like to understand climate variability as dynamical processes involving forcing-response-feedbacks (and so on) globally interacting with regional behaviors, etc.
After reaching a positive maximum of ~20 Hadleys (reanalysis data climatology from 1968-1997) just before October 1st, the global tendency of relative AAM has dropped to ~minus 10 Hadleys as of October 14th. As expected with a MJO, this positive AAM tendency started along/just south of the equator ~ September 18th, and has coherently propagated poleward into both hemispheres, particularly across the Northern Hemisphere (currently around 40N). A time-latitude section of 200mb zonal mean zonal wind anomalies loosely shows this poleward propagation, with westerly anomalies currently ~5-10m/s centered at about 30N (one level as opposed to a vertical integral).
After roughly October 1st there was relative AAM flux divergence from about 45N (sink) leading to flux convergence near 30N (source; we are looking at divergence of the AAM transports), again consistent with the dynamical signal of the MJO moving into the Western Hemisphere. This redistribution of AAM helped to weaken the midlatitude flow while increasing the westerly flow across the subtropics (including the STJ). A forecaster looking at a polar stereographic projection map of 250mb total vector winds (for example) would have observed a split flow pattern along the North American West Coast at times during this period as a response.
The point is using monitoring tools such as AAM tendencies and transports allows some understanding of the recent increases of the zonal mean westerly flow throughout the subtropical and midlatitude atmospheres. Through tropical-extratropical interactions involving the midlatitude synoptic eddies (reader needs to think about this) not only have we seen the central and east Pacific basin wide surface westerly wind event (discussed above), there has also been a strengthening of the North Pacific jet over the last 1-2 weeks, the latter having seven-day mean anomalies of ~20m/s. For the USA the result has been recent PNA responses (from Rossby wave energy dispersions -- index sign depends on location of features; one weakness of it) and an enhanced STJ all contributing to recent cool outbreaks for the central states and heavy rain for the Deep South. Please see our recent weather-climate discussion dated August 18th as an example to interpret some of these behaviors (link below).
The enhanced surface westerlies across the north tropical Pacific Ocean basin for at least the past 1-2 weeks has brought the global frictional torque down to around minus 20 Hadleys, and the global mountain torque is also starting to decline (see ESRL/PSD plots for details). GSDM Stage 2 would best describe the weather-climate situation from roughly October 1-14 (at times tilting toward Stage 3), with a loose GSDM Stage 4 the last few days. Animations of 150mb and 250mb daily mean vector wind anomalies once again present a strong signal of anomalous twin tropical/subtropical anticyclones around 160E tied to the tropical convective flare-up in that region (with well defined twin cyclones ~90E tied to the suppression; this is a baroclinic process). A Rossby wave energy dispersion is in progress and will lead to another PNA. This has some similarities to what occurred around October 8th, except the MJO dynamical signal is now in the Western Hemisphere, as opposed to the west Pacific. In fact, upper tropospheric easterly wind anomalies of ~20-30m/s at 150mb have been appearing across the equatorial east Pacific during the last few days, having more consistency with Stage 4 as opposed to Stage 2. This all suggests a retrogression of existing circulation anomalies during the next few days or so across the northern extratropics particularly from Asia-North America (“bottom line”).
To summarize, I think we have 1) a warm event (with the understanding of Indian Ocean-Pacific SSTs) whose future evolution still remains unclear (but likely to persist into 2007), 2) at least a moderate MJO signal moving across the Western Hemisphere, 3) intensifying tropical convective forcing from the Indian Ocean, 4) a mountain-frictional torque index cycle, 5) baroclinic wave packets/fast Rossby wave energy dispersions interacting with the west central Pacific tropical forcing, and 6) seasonal cycle issues.
There are other matters I am unclear about such as any sub-monthly component involving the mountain torque and other faster modes of tropical convective variability. The future of the MJO even after week 1 is also unclear. I do think the dominant forcing from the tropics is coming from the west central Pacific, and it may not just be a warm ENSO signal. The SSTs are also cool across the tropical northwest Pacific (opposite of last year) and the evolution of this whole “SST situation” is anything but trivial to understand. It would be interesting to see how well coupled GCMs would simulate these SST events since the start of this year.
In any case, we must also remember the suppression from Indonesia also has circulation impacts, and I can easily see Indian Ocean tropical forcing disrupting events across the west Pacific. The statistical models (Wheeler phase space technique, for example) bring the dynamical signal well into the Eastern Hemisphere (~60-80E) by about day 10, and I think that is reasonable. My own thoughts is there may be 2 well defined regions of enhanced tropical convection during week 2, the Indian Ocean and west central Pacific, while the Western Hemisphere becomes suppressed. During week 3 there may be some consolidation of the 2 regions north of the cool SSTs across Indonesia. Confidence in any scientifically defensible statistically useful prediction particularly beyond week 1 is as low as it gets. This is the real world!
Week 1 (18-24 October 2006): I think a loose rendition of GSDM Stage 2 is most probable, but roughly 5-10 degrees farther west (for the USA) than about a week ago. This would mean a trough ~100W with a large amplitude ridge just off the USA west coast possibly into Alaska. Nearly all models are predicting some version of this response since the Rossby wave energy dispersion discussed above should be in the initial conditions. This means a much cooler than normal regime for a good part of the country especially the central and north central states. The warm locations may be the West Coast and Florida. One surge of cool air is occurring as I type, with another due by this weekend per operational NCEP GFS (and other models).
I have a bit of concern for this second surge of cool air. The jet streak that will contribute to it (interacting with “everything else”) may involve the remnants of Typhoon Soulik. The baroclinic development which ensures on the Plains by this weekend may begin with amplification of the trough a bit farther west into the central Rockies. That may suggest more robust cyclogenesis across the Mid/Upper Mississippi Valley. Even though moisture will be relatively limited, a “decent” snow event is not out of the realm of possibilities for locations such as Iowa into the Great Lakes (latter including lake effect). Other effects on the weather should be apparent.
The Tropical North Atlantic may remain suppressed for tropical cyclone activity. There is always the concern for hybrids this time of year and I could also see a period of upper tropospheric easterlies across the tropical Atlantic, latter perhaps allowing a window of opportunity for development. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information. Active regions for tropical cyclones may include the west central Pacific and even the Bay of Bengal, particularly weeks 2-3.
Week 2 (25-31 October 2006): If the west Pacific is “calling the shots”, then similar to week 1 except for the usual synoptic variations of amplitude.
Week 3 (1-7 November 2006): I can envision possibilities (like anyone else), but let us just say “unclear” for now.
Climatologically this is the dry time of the year for Southwest Kansas. Other than one or two minor episodes of precipitation, week 1 looks generally cool and dry. There is a small possibility of a “surprise” this weekend. I would expect week 2 to remain generally dry with roughly seasonable temperatures (on average!). Even though not discussed for week 3, opportunities for precipitation may increase for this part of the world should “STJ activity” become more robust.
Since I continue to have to cover lots of shifts (including mids), I may not be able to update this Blog until late next week. We do have plans to write another weather-climate discussion for the ESRL/PSD MJO web page to hopefully post by the end of November. 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), along with all the other issuances, has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Ed Berry
The spatial distribution of global tropical SST anomalies continues to resemble a mature warm event, with positive values across the western Indian Ocean and along the equator from ~140E-South America with cool readings around Indonesia particularly south of the equator. In fact, the SST horse shoe pattern of cool surrounding warm anomalies (would be reversed for a cold event) across the tropical Indo-Pacific is quite well defined. Anomalies are generally from 1-2C with magnitudes around 3C along the East Pacific cold tongue, extending to depths of ~200m around the date line. SSTs of 29C and warmer cover much of the equatorial date line region, the central Indian Ocean and both sides of Central America. Weak positive SST anomalies cover most of the tropical Atlantic with actual temperatures ~28-29C.
SST and SST anomaly tendencies during the past week or so have reinforced the spatial distribution discussed above. Magnitudes have been ~plus .5-1C, with the warming along the equatorial cold tongue the result of a basin-wide surface westerly wind event whose anomalies have exceeded 10m/s (more said below). At this point our warm event has become better defined during the past 1-2 weeks. I have expressed concern in past writings this event may have already peaked. Whether or not this is the case, is unclear to me, as is the future for this warm ENSO (there are seasonal cycle issues). Whatever the case, the SSTs linked to this ENSO evolution have already impacted synoptic variability across North America since at least June 2006, and are doing so as I type.
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/
Per coherent modes and velocity potential Hovmollers (and other monitoring tools), the dynamical signal with the MJO is in the Western Hemisphere ~0/60W having a phase speed of ~10-15m/s. The MJO signal typically propagates eastward much faster across the Western Hemisphere due to less air/sea coupling with cooler SSTs (loosely acting like a Kelvin wave enhancing upper tropospheric divergence). Full disk satellite imagery shows quite a bit of convective enhancement centered on northern South America with OLRAs ~minus 50-90W/m**2. The recent heavy rainfall across the USA Deep South had a contribution from this MJO signal as the result of a local enhancement of the subtropical jet (STJ) via complex interactions with the extratropics.
Well defined twin upper tropospheric subtropical anticyclones are present around 90-120W (including the Gulf of Mexico) with wind speed anomalies ~20-30m/s per animations of 150mb daily mean vector wind anomalies. Additionally, Rossby wave energy is dispersing into the extratropics of both hemispheres leading to, for example, a negative projection onto the North Atlantic Oscillation (NAO).
Full disk satellite imagery also shows tropical convection increasing across the west central Pacific centered ~0/150-160E as well as the equatorial Indian Ocean ~60E, while strong suppression remains across Indonesia with positive values of OLRA in excess of 70 W/m**2 ~0/100E. This spatial pattern of enhancement-suppression-enhancement across the Eastern Hemisphere would be expected from the SSTs, with the former termed by some folks as a positive phase of the Indian Ocean Dipole (IOD) and the latter due to ENSO. It is typical to see a warm western Indian Ocean during a mature warm ENSO, and I like to understand climate variability as dynamical processes involving forcing-response-feedbacks (and so on) globally interacting with regional behaviors, etc.
After reaching a positive maximum of ~20 Hadleys (reanalysis data climatology from 1968-1997) just before October 1st, the global tendency of relative AAM has dropped to ~minus 10 Hadleys as of October 14th. As expected with a MJO, this positive AAM tendency started along/just south of the equator ~ September 18th, and has coherently propagated poleward into both hemispheres, particularly across the Northern Hemisphere (currently around 40N). A time-latitude section of 200mb zonal mean zonal wind anomalies loosely shows this poleward propagation, with westerly anomalies currently ~5-10m/s centered at about 30N (one level as opposed to a vertical integral).
After roughly October 1st there was relative AAM flux divergence from about 45N (sink) leading to flux convergence near 30N (source; we are looking at divergence of the AAM transports), again consistent with the dynamical signal of the MJO moving into the Western Hemisphere. This redistribution of AAM helped to weaken the midlatitude flow while increasing the westerly flow across the subtropics (including the STJ). A forecaster looking at a polar stereographic projection map of 250mb total vector winds (for example) would have observed a split flow pattern along the North American West Coast at times during this period as a response.
The point is using monitoring tools such as AAM tendencies and transports allows some understanding of the recent increases of the zonal mean westerly flow throughout the subtropical and midlatitude atmospheres. Through tropical-extratropical interactions involving the midlatitude synoptic eddies (reader needs to think about this) not only have we seen the central and east Pacific basin wide surface westerly wind event (discussed above), there has also been a strengthening of the North Pacific jet over the last 1-2 weeks, the latter having seven-day mean anomalies of ~20m/s. For the USA the result has been recent PNA responses (from Rossby wave energy dispersions -- index sign depends on location of features; one weakness of it) and an enhanced STJ all contributing to recent cool outbreaks for the central states and heavy rain for the Deep South. Please see our recent weather-climate discussion dated August 18th as an example to interpret some of these behaviors (link below).
The enhanced surface westerlies across the north tropical Pacific Ocean basin for at least the past 1-2 weeks has brought the global frictional torque down to around minus 20 Hadleys, and the global mountain torque is also starting to decline (see ESRL/PSD plots for details). GSDM Stage 2 would best describe the weather-climate situation from roughly October 1-14 (at times tilting toward Stage 3), with a loose GSDM Stage 4 the last few days. Animations of 150mb and 250mb daily mean vector wind anomalies once again present a strong signal of anomalous twin tropical/subtropical anticyclones around 160E tied to the tropical convective flare-up in that region (with well defined twin cyclones ~90E tied to the suppression; this is a baroclinic process). A Rossby wave energy dispersion is in progress and will lead to another PNA. This has some similarities to what occurred around October 8th, except the MJO dynamical signal is now in the Western Hemisphere, as opposed to the west Pacific. In fact, upper tropospheric easterly wind anomalies of ~20-30m/s at 150mb have been appearing across the equatorial east Pacific during the last few days, having more consistency with Stage 4 as opposed to Stage 2. This all suggests a retrogression of existing circulation anomalies during the next few days or so across the northern extratropics particularly from Asia-North America (“bottom line”).
To summarize, I think we have 1) a warm event (with the understanding of Indian Ocean-Pacific SSTs) whose future evolution still remains unclear (but likely to persist into 2007), 2) at least a moderate MJO signal moving across the Western Hemisphere, 3) intensifying tropical convective forcing from the Indian Ocean, 4) a mountain-frictional torque index cycle, 5) baroclinic wave packets/fast Rossby wave energy dispersions interacting with the west central Pacific tropical forcing, and 6) seasonal cycle issues.
There are other matters I am unclear about such as any sub-monthly component involving the mountain torque and other faster modes of tropical convective variability. The future of the MJO even after week 1 is also unclear. I do think the dominant forcing from the tropics is coming from the west central Pacific, and it may not just be a warm ENSO signal. The SSTs are also cool across the tropical northwest Pacific (opposite of last year) and the evolution of this whole “SST situation” is anything but trivial to understand. It would be interesting to see how well coupled GCMs would simulate these SST events since the start of this year.
In any case, we must also remember the suppression from Indonesia also has circulation impacts, and I can easily see Indian Ocean tropical forcing disrupting events across the west Pacific. The statistical models (Wheeler phase space technique, for example) bring the dynamical signal well into the Eastern Hemisphere (~60-80E) by about day 10, and I think that is reasonable. My own thoughts is there may be 2 well defined regions of enhanced tropical convection during week 2, the Indian Ocean and west central Pacific, while the Western Hemisphere becomes suppressed. During week 3 there may be some consolidation of the 2 regions north of the cool SSTs across Indonesia. Confidence in any scientifically defensible statistically useful prediction particularly beyond week 1 is as low as it gets. This is the real world!
Week 1 (18-24 October 2006): I think a loose rendition of GSDM Stage 2 is most probable, but roughly 5-10 degrees farther west (for the USA) than about a week ago. This would mean a trough ~100W with a large amplitude ridge just off the USA west coast possibly into Alaska. Nearly all models are predicting some version of this response since the Rossby wave energy dispersion discussed above should be in the initial conditions. This means a much cooler than normal regime for a good part of the country especially the central and north central states. The warm locations may be the West Coast and Florida. One surge of cool air is occurring as I type, with another due by this weekend per operational NCEP GFS (and other models).
I have a bit of concern for this second surge of cool air. The jet streak that will contribute to it (interacting with “everything else”) may involve the remnants of Typhoon Soulik. The baroclinic development which ensures on the Plains by this weekend may begin with amplification of the trough a bit farther west into the central Rockies. That may suggest more robust cyclogenesis across the Mid/Upper Mississippi Valley. Even though moisture will be relatively limited, a “decent” snow event is not out of the realm of possibilities for locations such as Iowa into the Great Lakes (latter including lake effect). Other effects on the weather should be apparent.
The Tropical North Atlantic may remain suppressed for tropical cyclone activity. There is always the concern for hybrids this time of year and I could also see a period of upper tropospheric easterlies across the tropical Atlantic, latter perhaps allowing a window of opportunity for development. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information. Active regions for tropical cyclones may include the west central Pacific and even the Bay of Bengal, particularly weeks 2-3.
Week 2 (25-31 October 2006): If the west Pacific is “calling the shots”, then similar to week 1 except for the usual synoptic variations of amplitude.
Week 3 (1-7 November 2006): I can envision possibilities (like anyone else), but let us just say “unclear” for now.
Climatologically this is the dry time of the year for Southwest Kansas. Other than one or two minor episodes of precipitation, week 1 looks generally cool and dry. There is a small possibility of a “surprise” this weekend. I would expect week 2 to remain generally dry with roughly seasonable temperatures (on average!). Even though not discussed for week 3, opportunities for precipitation may increase for this part of the world should “STJ activity” become more robust.
Since I continue to have to cover lots of shifts (including mids), I may not be able to update this Blog until late next week. We do have plans to write another weather-climate discussion for the ESRL/PSD MJO web page to hopefully post by the end of November. 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), along with all the other issuances, has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Ed Berry
Wednesday, October 11, 2006
Weather-Climate Update
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, and this one will be short due to shift work obligations.
SSTs have changed little since my posting on October 6th. There is some evidence that the current warm phase of ENSO is peaking.
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 dynamical signal with the MJO is propagating through the Western Hemisphere, with a phase speed of 10-15m/s based on Hovmollers of velocity potential and OLRA. This is an increase from about 2 weeks ago, and is typical when the MJO signal moves into the Western Hemisphere. Full disk satellite imagery suggests the dynamical signal is centered around 0/80W. Surface westerly wind anomalies of 10-20m/s have propagated northward from the equatorial date line region and have contributed to anomalous westerly flow across much of the North Pacific at ~30N during the last few days. The latter was theresult of 2 tropical convective flare-ups and westerly wind events during the last 10-14 days, and has been associated with tropical cyclone activity across the West Pacific. In fact, there is a signal in the global AAM tendency of the tropical convective flare-ups associated with the MJO.
In the upper troposphere, 200mb zonal mean zonal wind anomalies of ~5m/s are presently centered ~20N, and there is evidence of meridional symmetry. Additionally, some linkage between the anomalous zonal mean westerly flows throughout the subtropical and midlatitude atmospheres has occurred during the last few days. Loosely, GSDM Stage 2 (tilted toward Stage 3) best describes the weather-climate situation during the past week. This has impacted the USA in the form of the currently strong positive phase of the Pacific-North American teleconnection (PNA). A major cold outbreak (for this time of year) into the North Central states is occurring as a response.
Strong suppression exists across much of the Eastern Hemisphere while convection remains perhaps coupled to the warm SSTs just west of date line, oriented north-south across the equator over the 29C and greater SSTs. The latter region has been weakening after the development of Tropical Cyclone Soulik. Most of the tropical convective enhancement is along the East Pacific ITCZ (where SSTs are also warm) into the South Atlantic Convergence Zone (SACZ) and spreading into the tropical North Atlantic ITCZ. This activity is associated with "wavy" upper tropospheric westerly wind anomalies that normally develop downstream of tropical forcing over the Eastern Hemisphere.
My thoughts are for the dynamical signal to propagate into the Eastern Hemisphere by the week 2-3 time frame, and reinvigorate the tropical convection across much of the Indian Ocean (where are SSTs are also quite warm with anomalies ~plus 0.5-1C over greater than 29C water). SST boundary forced tropical convection would also be expected to continue just west of the date line. A rendition of GSDM Stage 4-1 may be probable during weeks 2-3, loosely suggesting a retrogression of existing circulation anomalies with the continuation of subtropical jets. Many numerical ensemble prediction systems are capturing this scenario for much of the northern extratropics for week 2.
Ramifications would include the possibility of an anomalously deep trough across the western USA (with a subtropical jet), along with a strong southwest flow storm track across the Plains and central portions of the country. While synoptic details are unclear (ex., the magnitude of any baroclinic cyclogenesis), there exists the possibility of an early season major winter-like storm for the Central and Northern Rockies (there will be a cold air source). Meanwhile, severe local storms and widespread rainfall (some heavy) would be possible for locations from the Plains into the Upper Mississippi/Ohio Valleys and Great Lakes states. Other weather anomalies from this type of pattern should be well known by now.
I hope to post a more complete discussion roughly a week from today.
Ed Berry
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 and additional components.
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
We hope to post another writing on the ESRL/PSD MJO web site within the next 4-6 weeks.
SSTs have changed little since my posting on October 6th. There is some evidence that the current warm phase of ENSO is peaking.
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 dynamical signal with the MJO is propagating through the Western Hemisphere, with a phase speed of 10-15m/s based on Hovmollers of velocity potential and OLRA. This is an increase from about 2 weeks ago, and is typical when the MJO signal moves into the Western Hemisphere. Full disk satellite imagery suggests the dynamical signal is centered around 0/80W. Surface westerly wind anomalies of 10-20m/s have propagated northward from the equatorial date line region and have contributed to anomalous westerly flow across much of the North Pacific at ~30N during the last few days. The latter was theresult of 2 tropical convective flare-ups and westerly wind events during the last 10-14 days, and has been associated with tropical cyclone activity across the West Pacific. In fact, there is a signal in the global AAM tendency of the tropical convective flare-ups associated with the MJO.
In the upper troposphere, 200mb zonal mean zonal wind anomalies of ~5m/s are presently centered ~20N, and there is evidence of meridional symmetry. Additionally, some linkage between the anomalous zonal mean westerly flows throughout the subtropical and midlatitude atmospheres has occurred during the last few days. Loosely, GSDM Stage 2 (tilted toward Stage 3) best describes the weather-climate situation during the past week. This has impacted the USA in the form of the currently strong positive phase of the Pacific-North American teleconnection (PNA). A major cold outbreak (for this time of year) into the North Central states is occurring as a response.
Strong suppression exists across much of the Eastern Hemisphere while convection remains perhaps coupled to the warm SSTs just west of date line, oriented north-south across the equator over the 29C and greater SSTs. The latter region has been weakening after the development of Tropical Cyclone Soulik. Most of the tropical convective enhancement is along the East Pacific ITCZ (where SSTs are also warm) into the South Atlantic Convergence Zone (SACZ) and spreading into the tropical North Atlantic ITCZ. This activity is associated with "wavy" upper tropospheric westerly wind anomalies that normally develop downstream of tropical forcing over the Eastern Hemisphere.
My thoughts are for the dynamical signal to propagate into the Eastern Hemisphere by the week 2-3 time frame, and reinvigorate the tropical convection across much of the Indian Ocean (where are SSTs are also quite warm with anomalies ~plus 0.5-1C over greater than 29C water). SST boundary forced tropical convection would also be expected to continue just west of the date line. A rendition of GSDM Stage 4-1 may be probable during weeks 2-3, loosely suggesting a retrogression of existing circulation anomalies with the continuation of subtropical jets. Many numerical ensemble prediction systems are capturing this scenario for much of the northern extratropics for week 2.
Ramifications would include the possibility of an anomalously deep trough across the western USA (with a subtropical jet), along with a strong southwest flow storm track across the Plains and central portions of the country. While synoptic details are unclear (ex., the magnitude of any baroclinic cyclogenesis), there exists the possibility of an early season major winter-like storm for the Central and Northern Rockies (there will be a cold air source). Meanwhile, severe local storms and widespread rainfall (some heavy) would be possible for locations from the Plains into the Upper Mississippi/Ohio Valleys and Great Lakes states. Other weather anomalies from this type of pattern should be well known by now.
I hope to post a more complete discussion roughly a week from today.
Ed Berry
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 and additional components.
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
We hope to post another writing on the ESRL/PSD MJO web site within the next 4-6 weeks.
Friday, October 06, 2006
MJO is for Real; Large Uncertainty Remains for the Future of our Warm Event
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
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
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
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