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 has not changed significantly during the past week or so, still resembling a mature warm event. Positive anomalies remain across the western Indian Ocean and along the equator from ~170E-South America with cool readings around Indonesia particularly south of the equator. There has been some warming of SSTs around Indonesia into the Bay of Bengal and Arabian Sea extending to just southeast of Asia, as well as northwest of Australia, with positive tendencies ~0.5-1.0C during the past week. The latter may be a direct result of solar input due to the strong convective suppression present there.
SST anomaly magnitudes as low as ~minus 2C remain just south of Indonesia on 3 November while ~plus 2C were observed just east of the equatorial date line and west of South America (keep in mind the seasonal cycle of SSTs). These positive SST anomalies are deep with plus 4C and greater observed at ~150m/165W per five-day averaged TAO buoy data ending 3 November. A recent surface westerly wind burst linked to the last MJO event appears to have initiated a down welling oceanic Kelvin wave currently approaching 160W along the equator.
The SST horse shoe pattern of cool surrounding warm anomalies (would be reversed for a cold event) across the tropical Indo-Pacific remains (axes of SST anomalies), and is best defined across the Southern Hemisphere with values ~minus 1-2C. Interestingly, there is anomalous SST warmth emanating from the Indian Ocean encasing the cool anomalies across both hemispheres including the extratropics.
Overall, the spatial coverage of above average global SSTs (tropics and extratropics) exceeds those which are cooler than normal. Much of the midlatitude South Pacific Ocean has below normal SSTs as a response to cooling from an intense baroclinic storm track since at least May 2006. It is my feeling that anomalous surface cross equatorial cool southerly flow from the deep southern extratropics into Indonesia starting around May 2006 linked to this storm track activity played a critical role to the evolution of our stochastically forced warm event. Please remember that in the tropics the SSTs generally force the atmosphere with the opposite for the extratropics (yes, everything understood).
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. The warm ENSO conditions are here to stay for at least the next 3-6 months. It is now a matter of how the spatial patterns of the SSTs evolve, and no two warm events (or anything else that occurs in the coupled global ocean-atmosphere, etc. system) are alike. The predictability of these kinds of details on the seasonal time scale is noise, as are the weather impacts.
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 all but gone. Per full disk satellite imagery and other tools enhanced tropical convective forcing remains most intense around 0/160E (OLRA~ minus 90W/m**2), with two other regions from Africa into the central Indian Ocean and the last from the Amazons and SACZ into the Atlantic ITCZ. The convection across the west central Pacific has been shifting west during the last week, weakly projecting onto a convectively coupled Rossby mode. Some consolidation of forcing is possible during the next couple of weeks north of Indonesia, and particular attention will need to be paid from the Bay of Bengal to the Philippines should this occur.
In general, as has been true since ~2002, it appears probable that we may have to deal with 2 regions of tropical convective forcing (and a weak, if any, MJO signal) again for this upcoming boreal winter, with the warm ENSO signal possibly dominating. I would expect to see coherent tropical convective forcing evolve and propagate east, but perhaps much faster than MJOs (Kelvin waves), and maybe other “MJO-like” behaviors (see our weather-climate discussions). Is the latter the result of a longer term trend such as global warming (what I termed as a “new world atmosphere” in past postings)?
Since about Halloween, tied to the past MJO, there has been fairly coherent poleward propagation of zonal mean zonal westerly wind anomalies with magnitudes up to 15m/s ~35N at 200mb during the past couple of days. Zonal mean upper tropospheric easterly wind anomalies have become dominate within 10 degrees of the equator during the past week (and also from ~45-60N). Global relative AAM has become slightly negative (~minus .5 sigma per operational data), with much of that coming from the global mountain torque of ~minus 15 Hadleys. I can attribute some of this as the result of anomalously low mean sea level pressures along the east slopes of north-south mountain ranges for both the tropics and extratropics impacted by the poleward propagation of the zonal mean anomalous westerlies discussed above. The reason is not only have these westerlies been propagating poleward, but also downward through the troposphere, eventually reaching the surface. There have also been complex interactions with much faster time scales such as the mid-latitude eddies that have subsequently impacted the tropical convection (which has also contributed to recent lowering of mean sea level pressures across the deep tropics).
In terms of the tropical forcing and AAM budget, GSDM Stage 4 may best describe the current situation. However, as shown by the ESRL/PSD animations of both 150mb and 250mb daily mean vector wind anomalies, with magnitudes of roughly 15-30m/s, twin tropical/subtropical cyclones cover much of the Indian Ocean while anticyclones rule over the central Pacific centered around the date line. Centered ~40N, a large anomalous cyclonic gyre covers much of the North Pacific Ocean basin supporting enhanced westerlies ~30-35N (consistent with the poleward propagation discussed above). In fact, a weekly average of 150mb vector wind anomalies ending 4 November suggests a coherent residual of Rossby wave energy dispersion linked to the west central Pacific tropical forcing arcing to a blocking pattern across the North Atlantic (which would project onto a reverse NAO and explain some of the current zonal mean anomalous higher latitude easterly flow). Thus in terms of the actual global circulation GSDM Stage 3 may apply (suggesting split flow across North America).
This kind of response can be expected from a warm ENSO, and may be a pre-cursor to the type of circulation pattern for this upcoming boreal winter. For the USA, during the past week we have seen precipitation increase along the west coast from northern California to Alberta (yes, Canada) while much of the rest of the country has turned warmer and dryer. Back to the GSDM, I would offer Stages 3-4 for the current situation.
To summarize, I think we have 1) a warm event (plus a global warming signal whose cause is unclear?), 2) an increasing role of the Indian Ocean SSTs, 3) the MJO signal which has become very weak, 4) 20-30 day tropical convective variability (not discussed), 5) some evidence of mountain-frictional torque index cycle variations (also not discussed – may be linked to (4)), fast RWDs, baroclinic wave packets and all sorts of other white noise, and 6) seasonal cycle issues.
As stated above, we may be seeing an early November rendition of an expanded East Asian Jet (EAJ). There are countless sensitivity issues discussed in past postings and weather-climate discussions. I also did not discuss how our GSDM Stage 3 (like?) circulation may have come about over the past week due to complexity. Short story is that in addition to the tropical forcing discussed above, tied to East Asian baroclinic wave packets, there was also a flare-up if convection around the Philippines (Tropical Northwest Pacific) that led to former Super Typhoon Cimarron. This forcing also added westerly flow. With that convection “gone” and at least some consolidation (see above) by around week 2, I think the North Pacific Jet will retract. This is just one of the sensitivity matters the current numerical models are struggling with in terms of predictions.
During this upcoming week, a split flow pattern should remain across the country. Most of the precipitation looks to occur along the west coast (mainly Pacific Northwest) and eventually across the Deep South. The latter will depend on just how much baroclinic development occurs along the southern westerlies. Whatever the case may be, a cold air source looks to be lacking.
For weeks 2-3, GSDM Stage 1 may evolve, meaning a full latitude trough with an Arctic cold air source (monitoring does show some recent build up – recall where the blocks are) would become increasingly probable for the western half of the country. There may also be an active subtropical jet tied to the warm ENSO. This would be a very active weather regime (including possible high-impact events such as blizzard conditions and severe local storms) for this time of year across a good part of the country (including a southwest flow storm track across the middle). I think the readers are familiar what the weather would be from all this.
Work is on-going to write another weather-climate discussion for the ESRL/PSD MJO web page. Since it would be ideal to have this discussion posted before attending the 4-8 December 2006 THORPEX meeting in Germany, it will be difficult for me to do these postings weekly. Please keep checking, and see the Appendix.
Appendix
The following is a link to our MWR paper that discusses the GSDM (Weickmann and Berry 2006, in press).
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
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