Friday, June 08, 2007

Update on a Stalled Atmosphere

Reanalysis-1 (R1) data flow problems into ESRL/PSD have been solved meaning the AAM and GSDM/GWO plots are being reasonably updated .

This posting will be abbreviated due to time constraints. There has not been much change to the global distribution of tropical and subtropical SSTs since 6/4. Weak cool anomalies have developed across portions of the Arabian Sea in the wake of Severe Hurricane (Category 5 on the Saffir-Simpson Scale) Gonu. In fact, even though Gonu may have been the strongest tropical cyclone on record in that region, there was a weak MJO related week-1 signal to predicting the possibility of the occurrence of at least a tropical cyclone in that region. SST anomalies have dropped to at least ~minus 2C west of South America along the Pacific cold tongue (down to ~200m to 160W per TAO data) while some warming has occurred across the equatorial Atlantic. The development of La-Nina remains unclear, especially since the tropical west Pacific Ocean remains above normal (stated scientifically, understanding other discussions on this matter). The recent increase in the trades across that region may lead to respectable cooling there (as a response to the recent Indian Ocean convection).

I think the MJO dynamical signal remains stalled in the region of Africa per several monitoring tools such as OLR and upper tropospheric velocity potential. Tropical convection has been getting better organized ~5N/40-60E during the last few days. Per full disk satellite imagery enhanced rainfall covers much of the Arabian Sea into the Indian Monsoon region (3 day averaged OLRA ~minus 50 W/m**2 per BMRC). There has been suppression from Southeast China into the west Pacific. However, intense clusters of thunderstorms are rapidly developing across the “dangerous” west central and tropical northwest Pacific Ocean. Twin upper tropospheric tropical anticyclones have been intensifying across the Indian Ocean. Additionally, there has been a general increase in upper tropospheric zonal mean anomalous easterly wind flow throughout the deep tropical and subtropical atmospheres over the last few days, particularly north of the equator. Anomalous zonal mean westerly flow remains ~30-35 N and S (~10m/s at 200mb).

The global weather-climate situation remains solidly in GSDM Stage 1. As shown by the GWO phase space plot, there has been a recent small orbit due to the latest mountain/frictional torque index cycle. Interestingly, there has been a drift toward the right side of this plot during the last few months. I speculate contributions to this drift (meaning a slow increase in westerly flow throughout the atmosphere) have come from the mountain/frictional torque index cycles as well as the west Pacific Ocean tropical convection.

It is probable the MJO dynamical signal will drift east and north (typical of boreal summer) during the next few weeks, possibly reaching the warm west and northwest Pacific Ocean during weeks 3-4. It is also probable there will be separate flare-ups across the west Pacific Ocean within our stationary to slowly evolving GSDM Stage 1 atmosphere. This suggests the Indian Monsoon will remain active, while the Indo-China and Southeast Asian regions possibly intensify. Tropical cyclone risks may increase southeast of the Philippines by ~week 3.

More strong western USA troughs with downstream south central-eastern states ridging will continue for at least the next 10 days. Related to the seasonal cycle, perhaps by ~week 3 a trough may become established around the Pacific Northwest supporting intense summertime ridging across particularly the south central/central USA. Many numerical ensemble prediction systems have been suggesting ridge conditions over the Desert Southwest by week 2, attributable as a “pre-monsoon” signal by some. The latter is not a meteorological reason, in terms of the dynamics of subseasonal variability including the behaviors described by GSDM. In fact, I can easily see more strong troughs impacting the Pacific Northwest into the Plains going into July. Weather ramifications for the USA I think are understood.


An experimental phase space plot of the GSDM (depicting a global wind oscillation) utilizing normalized relative AAM time tendency (Y-axis) and normalized relative AAM (X-axis) can be found at

These are probabilistic statements, and work is ongoing to quantify in future posts. I hope the opportunity will arise soon to have a dedicated web page effort for our work. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to write a discussion early next week.

Ed Berry

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