Sunday, June 25, 2006

The Tune Continues

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

The gist is that from taking into consideration the interactions of 4 different subseasonal time scales, a sequence 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.

Due to time and technical difficulties/resource limitations on my end, this will be an abbreviated posting. Please see links from the June 22nd discussion.

The discussion issued last Thursday (6/22) is on track. The tropical convective forcing has essentially consolidated ~5-10N/110E, and extends from the northern Arabian Sea east-southeast into Indonesia and the west Pacific. The southeast Asian and Indian Monsoon systems appear to be quite active. I think this tropical convective forcing is evolving into at least a weak MJO, and that notion is getting more support from several monitoring tools. During the past week-10 days there has been roughly a 20 deg. eastward shift along the equator of the loosely defined center (from ~90-110E), with poleward movement on the western flank, particularly for the Northern Hemisphere.

During the upcoming weeks attention needs to paid on how closely this (probable) developing MJO "hugs" the equator. Whether or not a westerly wind event (WWE) occurs on the equator as opposed to its north (as suggested by seasonally adjusted composites) is critical to the possibility of generating an oceanic Kelvin wave (Kw). The latter do contribute to development of central and east Pacific warm events (El-Ninos), but this MJO-WWE-oceanic Kw scenario is much more likely during the Northern Hemisphere fall. However, summer 2004 was a bit of an exception (see August 13th 2004 weather-climate discussion at

There is more evidence of a SST-tropical convective forcing-circulation response feedback process developing. For instance, near equatorial surface westerly wind anomalies prevail across the Indian Ocean (perhaps the beginning of a westerly wind event) while a trade wind surge is developing across the central and western Pacific. Additionally, while upper tropospheric zonal mean easterly wind anomalies continue to propagate well off the equator and into at least the Northern Hemisphere lower extratropical atmosphere (which will support strong subtropical ridges), westerlies ~10-15 m/s are present just north of the equator. With the tendency of global relative AAM strongly positive with contributions from at least the mountain and frictional torques, I think the global circulation has transitioned to GSDM Stage 2 (or will do so "shortly").

The week 1-3 forecasts issued last Thursday look good, except day 1 is June 26th with this posting. With the strengthening near equatorial zonal mean westerly anomalies appearing and even the "hint" of twin upper tropospheric cyclones across the Indian Ocean during the last day or so (per daily mean animations of 150mb vector wind anomalies), I think a summertime rendition of GSDM Stage 3 is looking a bit more probable later week 2 or 3. This would be a west and north shift of the Stage 3 North American split flow pattern observed during the colder season. We may observe a "Hudson's Bay low north of a subtropical southeastern USA high" with the split flow along or just west of the West coast going into week 3. Impacts may include suppression of the southwest USA monsoon (which may get quite active in the shorter term) and a strong MCS track across the northern and central part of the country.

Given the amplitude of the ridge, rain chances across Southwest Kansas do not look as good as I earlier thought at least through much of week 1 (Wednesday/Thursday). However, increasing lower latitude zonal mean westerly flow should improve our precipitation chances afterwards. Temperatures should average about normal for the next 2-3 weeks.

I will do my best to post a complete discussion on about next Wednesday.
Ed Berry

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