Friday, August 15, 2008

The Mess

The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”

Please keep in mind the ESRL/PSD GSDM web link, below, while reading this discussion.

The 91-day signal to noise ratio anomaly composites are now updated daily, centered on the date shown (see product descriptions). Stay tuned as our work slowly moves forward. Again, this effort is a work in progress with extremely limited resources.

There is little significant change to the global pattern of SSTs discussed a week ago. The warmest ocean waters are from the west central into the tropical northwest Pacific (totals ~29-30C), and anomalous warmth persists across the equatorial Indian Ocean. The positive SST anomalies east of 140W along the equatorial Pacific Ocean have increased to at least 1-3C, but with totals less than 27C. The latter anomalies are not trivial and are a significant concern for possible impacts on the inter-yearly component of global ocean-atmospheric variability, remembering seasonal cycle and interannual issues. See links below. (note the initial projection) (link 18)

The weather-climate situation is extremely complicated having mixed signals. Many different interpretations can be offered. Regardless, this is another example where “cookbook prediction techniques (including relying on the models alone)” and blanket statements like “ENSO neutral” are not scientifically complete efforts. I want to do my best to cut to the chase what rigorous daily monitoring within the WB (2008) GWO and WB (2007) GSDM frameworks are telling me.

Enhanced tropical convective forcing is concentrated in the region of India to Southeast Asia (~15-30N; shifted anomalously north similar to a year ago), the west central Pacific Ocean and around the Americas. The flare-ups continue across the west central equatorial Indian Ocean. Through 14 August WH (2004) phase space plots show a stationary projection of roughly 1 sigma in octants 1-2, and nearly 1.5 standard deviations in octant 2 leaving the very important interannual base state in. In fact, there has been a decided interannual shift toward the Indian Ocean during the last few months. Among other arguments, I think dynamical processes linked to our past low AAM base state (2007-08) are contributing to the west central equatorial Indian Ocean flare-ups.

Even though the WH (2004) plots show a projection in ~octant 2 in phase space, in reality some of the recent Western Hemisphere enhancement can be attributed to the July MJO event. In addition, driven largely by positive global mountain torques, particularly the East Asian component, there have been two recent ~10-20 day fast orbits in the WB (2008) GWO phase space. Specifically, ~6 August both the East Asian and global mountain torques were roughly plus 15 Hadleys (R1 data), with the former having an approximately 10-day periodicity. Through 13 August the torques remain positive, with a tendency for North America and East Asia to remain out of phase (an old base state issue). Broadly, the GWO orbits have involved phases 8-1 to 4-5.

The bottom line is I think extratropical Rossby wave energy dispersions (RWDs) involved with the fast GWO orbits contributed to both the Western Hemisphere signal (in addition to the MJO) and the west central Pacific Ocean tropical convection. AAM transports tied to the mountain torques have “helped” to shift zonal mean westerly wind flow anomalies off the equator to well into the subtropical atmospheres (~30N/20S). An extratropical PNA response has been an anomalous extension of the polar jet stream across the North Pacific Ocean (~45N/250mb wind speed anomalies roughly 30m/s) leading to west coast ridge amplification and a trough in the central USA. The latter is consistent with phase 4 of the GWO composite, and that was the location in phase space of the GWO ~7-9 August.

Zonal mean easterly wind flow anomalies are increasing across the global tropics, and phase 2 of the WH (2004) MJO composite streamfunction anomaly represents the tropics very well. During approximately next week, temperature composites on phases 8-1 of the WB (2008) GWO are reasonable, suggesting a western USA trough (models have caught this). I do think it is probable for the GWO and MJO locations in phase space to sync up during weeks 2-3, favoring octants 2-3. The attendant dynamical processes will drive global AAM to be below normal. I also suspect there will be a coherent eastward shift of this coupled tropical-extratropical forcing, possibly into the west central and northwest Pacific Ocean. The temperature and streamfunction anomalies shown by GWO/MJO composite phases 3-5 may be most representative for North America during weeks 3-4.

Finally, a serious subseasonal monitoring issue will be to see not only far east the above mentioned coupled forcing shifts, but also for subsequent events. Should strong tropical convective forcing initiate equatorial westerly wind bursts across the anomalously warm west central Pacific Ocean (and oceanic Kelvin waves), a change in the interannual base state may evolve. Until then (if at all), I favor a tilt toward a weakly low AAM base state having important subseasonal events. Having my reasons, the barrage of troughs into the western and central USA may resume boreal fall going into winter, but with additional subtropical westerly wind flow.

The solutions being served up by most models are reasonable through days 7-10. Among other impacts (should be understood), intense/severe MCS activity may return to the Northern Plains and Upper Mississippi Valley week-2. As suggested by the GSDM composites, troughs would then be more probable to deepen into the central states then shift east particularly weeks 3-4. The global circulation regime appears quite favorable for Atlantic Ocean tropical cyclogenesis for at least the next 1-2 weeks (already have Tropical Storm Fay).

Intense to severe tropical thunderstorm activity is probable to persist and even intensify across the Eastern Hemisphere monsoon systems of India and Southeast Asia through at least weeks 2-3. There will be the seasonal southward shift of this activity going into boreal autumn. The west central and northwest Pacific Ocean will be a wild card for numerous reasons until further notice, including the risk of tropical cyclones. Hopefully there will some Western Hemisphere suppression later week-2 and week-3.

Please see the latest official tropical cyclone forecasts for all basins. I trust the expertise of the appropriate meteorological centers to alert the public of additional weather hazards worldwide (there has been a recent increase).


Links to CPC and PSD ENSO discussions:

The following is a link to information about the stratosphere and other nice monitoring tools:

The following is a link to NCEP model verifications (surf around for lots more) .

The following is a link discussing recent global weather and related events.

These are probabilistic statements. We hope that an opportunity will arise for us (soon) to allow our dedicated web page effort to mature, expediting objectively and accountability. This web page effort will hopefully include an objective predictive scheme for the GWO with hindcasts.

The WB (2007) paper on the GSDM has been published in the February issue of MWR. In addition, the first of a two-part paper has been submitted to MWR where WB formally introduce the GWO. A pdf version can be downloaded from the following link:

Overlapping seasonally varying subseasonal composites for variables such as surface temperature, precipitation, geopotential height and streamfunction anomalies are planned on being posted on the web site mentioned above and presented in part-2 of our paper. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships. An important purpose is to provide a dynamical weather-climate linkage framework to evaluate the numerical models in a sophisticated manner as part of a subseasonal (and any time scale) forecast process, in addition to a climate service for all users. Relying on the numerical models alone is a cookbook!

Given shift work and travel, updates are extremely difficult. I hope to do another discussion next weekend, ~23-24 August.

Ed Berry

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