Thursday, November 09, 2006

War Resumes Between Good and Evil

Please see past postings for web site links. Also, I need to get very serious about paring down the length. Hopefully that will translate to more frequent but short discussions.

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 ~date line-South America with cool readings around Indonesia particularly south of the equator (see November 3rd posting for details). The warmest SSTs are still found along the equatorial date line with readings near 31C having ~2C anomalies. Equatorial SST and SST anomaly tendencies over the last week were ~minus 0.5-1.0C from around 140E-South America with some positive values across the Indian Ocean. Additionally, SST animations suggest there has been about a 10 degree eastward shift of the warm-cool-warm pattern discussed above during the last 2-3 months (seasonal cycle understood).

What is also interesting is the above average SSTs across the extratropical North Pacific Ocean basin. Granted, the latter have a secondary role to tropical SSTs (and different ocean-atmosphere dynamical processes – I need to keep down the length!). However, warm North Pacific SSTs is not consistent with a warm ENSO (in the composite sense), again keeping in mind the seasonal cycle. The latter could quickly change should GSDM Stage 3 evolve meaning a strong North Pacific jet with attendant East Asian cold air surges, etc., (which does not look probable for at least the next few weeks).

The following are links to ENSO discussions.

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.

The point I want to emphasize in this writing is our two regions of tropical convective forcing is back. One region extends from equatorial Africa into the central Indian Ocean with the other centered ~0/160E. Yes, there are those who will invoke the Indian Ocean Dipole (IOD) notions and offer this situation is not all that unusual for a warm ENSO. While there is truth to these concepts, from my monitoring of trying to understand the dynamics of ocean-atmosphere forcing-response-feedbacks involving many scales of motion making use of the GSDM framework, the current weather-climate situation is much more complicated. From looking at animations of daily mean 150mb and 250mb vector wind anomalies I can clearly see the extratropics interacting with both regions of tropical forcing while helping to maintain them. We need to also remember this current warm ENSO evolved in a very random (and unpredictable) manner.

There is evidence from various tools (ex., Hovmoller plots of 250mb meridional wind anomalies in the 10-40N/S latitude bands) that subtropical wave trains are currently present in both hemispheres. I also have a suspicion that the tropical forcing over Africa into the Indian Ocean is trying to evolve into another MJO (the Wheeler phase space plot supports this). We will see. Global relative AAM tendency as of November 6th was ~minus 20 Hadleys as zonal mean westerly wind anomalies propagate poleward to ~30N/S while being replaced by zonal mean easterly wind anomalies throughout the deep tropics (magnitudes ~5-15m/s at 200mb). GSDM Stage 4 still best describes our current weather-climate situation, and may go into Stage 1 during the next 1-3 weeks. Again, forecast uncertainty is about as high as it can get.

As we progress into the upcoming boreal winter, to me it will be interesting to watch how far east the above discussed SST anomaly pattern progresses. I do think there will continue to be 2 regions of tropical forcing (on average). We may also observe a fair frequency of GSDM Stages 4-1 as opposed to a persistent GSDM Stage 2-3 during January-February. Whatever the case, while a “simple” seasonal mean (DJF, for example) pattern of temperature and precipitation anomalies may emerge which many might attribute to warm ENSO, the variability may be anything but simple with a great deal of global high impact weather with contributions coming from other complex processes not well understood (which is one reason why no 2 warm and cold events are alike beyond the composite/statistical senses).

To summarize, I think we have 1) a warm event (plus a global warming signal, with cause still unclear(?)), 2) an increasing role of the Indian Ocean SSTs, 3) the possibility of a re-emerging MJO signal, 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, 6) increasing blocking at the higher latitudes which I can link to both regions of tropical forcing and 7) the always present seasonal cycle issues.

Amplification is occurring throughout much of the subtropics and extratropics from Asia-North America as I type. A residual of the once extended strong North Pacific jet (anomalies are ~30-40m/s ~40N east of the date line at 250mb) is likely to penetrate into much of the country during week 1. The models do show this; however, it is still unclear where and when any amplifying trough will occur. There is likely to be high impact weather for at least the Pacific Northwest (heavy rain) and Deep South/Ohio Valley (severe local storms, etc.) , and perhaps the Upper Mississippi Valley and Great Lakes for winter weather. Disciplined monitoring will be needed including the models as they “catch on”.

During weeks 2-3 a more “classic” GSDM Stage 1 (with subtropical jets) may be probable particularly if at least a “MJO-like” feature develops. That would be favorable for full-latitude troughs to penetrate into western North America having an Arctic cold air source. We should all know “what that means” by now.

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.


The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006, in press).

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

Ed Berry

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