Thursday, November 16, 2006

The Fist of El-Nino Continues (The Devil of the Tropics???)

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

The overall spatial distribution of global tropical SSTS still has warm anomalies across the Indian Ocean (IO) and central/eastern tropical Pacific (~plus 1-3C) with cool (but weakening) values across southern Indonesia. Warm anomalies also persist across the Atlantic. Actual SSTS of 30C and higher remain present around the date line with 29C and warmer across the Indian Ocean. The positive SST anomalies along the equatorial cold tongue extend to depths of roughly 150m with magnitudes ~plus 4C meaning a deeper than normal thermocline. Part of this SST distribution is from a well defined warm ENSO signal although there are other contributions.

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.

Loosely 3 regions of tropical convective forcing are present. Per full disk satellite imagery (and other monitoring tools) these areas are centered on the Americas, from Africa into the Indian Ocean and finally across the Southwest Pacific between the Polynesian Islands and Australia. There are indications the convection across the Indian Ocean may be evolving into a coherent eastward propagating feature, possibly an MJO. The tropical forcing across the South Pacific has shown a rapid increase during the last couple of days, likely a response to the warm SSTs (and interactions with the southern extratropics). The latter appears to be shifting to the west-northwest along the South Pacific Convergence Zone (SPCZ). The signal across the Western Hemisphere is at least partly a convectively coupled Kelvin wave.

The extratropics have been strongly impacted by this complex tropical forcing, with subsequent feedbacks. For instance, since late October zonal mean westerly wind anomalies (~5-15m/s at 200mb) have propagated from the tropical into the subtropical atmospheres (to ~30N) while being replaced by easterlies. Some of this poleward propagating westerly flow has made it to the surface (ex., the North Pacific Ocean) augmenting deep tropical moisture transport from the date line region to the USA Pacific Northwest where excessive rainfall has been occurring. Additionally, upper tropospheric divergent outflows from the African and Indian Ocean convection through interactions with baroclinic wave packets have led to the current blocking structure near Kamchatka. Per animations of 150mb and 250mb daily mean vector wind anomalies from ESRL/PSD, feedbacks from this blocking have assisted with the recent dynamic suppression of convection along and to the north of the equatorial date line (where SSTs are warm).

GSDM Stage 4 best describes the current weather-climate situation. Where we go from here remains very uncertain. Yesterday I thought a slow transition from GSDM Stage 4-1 was most probable during the next 1-3 weeks. However, I am now concerned about the recent very rapid increase of convection across the South Pacific (daily monitoring is critical!). Respect needs to be given to the warm SSTs in that region. My own thought would be to “expect” a convectively coupled feature to shift east from the Indian Ocean into the west central Pacific during the next 1-3 weeks, possibly consolidating with a convectively coupled Rossby wave around ~120-140E north of the equator. The latter may evolve from the South Pacific.

Thus I think GSDM Stage 1 is probable by week 2, but may give way to Stage 2 by/during early December. One option with this scenario would be for an eastward shift of existing circulation anomalies, meaning full latitude troughs with Arctic air to impact the western USA sometime during week 2. By week 3 these troughs may shift toward the Plains while a ridge amplifies off the North American coast into Alaska. This would suggest an active regime for the Plains (all impacts should be understood) week 2 followed by perhaps much colder than normal temperatures for much of the country starting early December (centered on the Plains/Upper Mississippi Valley). Locations such as the Pacific Northwest may get a break from excessive precipitation by that time. We will see what happens; including if/when GSDM Stage 3 makes its appearance (extended low latitude North Pacific combined jet with split flow across North America – “typical” of a warm ENSO).

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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