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 (snr) anomaly composites are now updated daily, centered on the date shown. Please see product descriptions.
Writing like the record that never stops playing, overall spatial patterns of global SSTs, tropical and extratropical, have changed little during the past several weeks. However, some warming has recently occurred across the equatorial west central and southwest
The anomalous warmth across the equatorial Indian Ocean has expanded during the last week, with totals in excess of 29C and anomalies at least plus 0.5-1C (large for the
http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)
Following through from my last discussion, 27 September, the tropics and extratropics appear to be getting back in sync. However, I think this dynamical process is occurring in the Western Hemisphere, perhaps from the
There have been several complicated dynamical processes that I have been observing leading to the current tropical-extratropical circulation coupling. It is nearly impossible for me to explain that level of detail in these discussions. In summary, these included 1) fast ~10-20 day global mountain-frictional torque index “cycles” since about 10 September, with roughly 10-20 Hadley variations for the global mountain torque; 2) meridional momentum transports, including a recent rapid quadrapole of zonal mean sinks and sources, forced by the eddies; 3) a slower ~50-day variation of the global frictional torque linked to the tropical convective forcing and dissipation of extratropical westerly wind flow anomalies in the storm track regions; and 4) Rossby wave energy dispersions (RWDs) excited by the tropical convective forcing. Inter-hemispheric meridional symmetry involving these processes has become quite robust.
The bottom line is that the WB (2008) measure of the GWO, a dynamical representation of the global circulation which considers the MJO, best explains the physical processes forcing the atmosphere. Interactions of the zonally oriented RWDs have literally dragged any MJO component of tropical forcing into the
All of these complicated processes have worked to bring global relative AAM down to about 1 sigma below the R1 data climatology through 2 October. With a computed tendency of ~minus 15 Hadleys, the WB (2008) GWO has done a rapid orbit to roughly octant 1 of phase space, following a slower evolving similar trajectory. Anomalous zonal mean easterly wind flow; for example, greater than 5m/s at 200mb ~15S, is returning to the tropical and subtropical atmospheres. The anomalous zonal mean westerly wind flow that propagated into the midlatitudes a few weeks ago is undergoing frictional dissipation (per above). The latter is why there was the large orbit in GWO phase space, from octants 4-5 to 8-1, during September. Furthermore, the decided ~1 sigma shift toward the low AAM portion of GWO phase space is a response to the tropical-extratropical coupling including a persistent negative global frictional torque since about mid-September.
Summing up, the global circulation has returned to a weakly low AAM base state. I have concerns that as tropical convective forcing becomes anomalously intense across the Indian Ocean into
Regionally for the PNA sector, GWO phases 8-1 of the 250mb psi snr composite anomaly plots best depicts the current circulation, while phases 2-3 for the MJO 250mb psi composites depicts tropical circulation anomalies. Recall that the global circulation is still “getting back together”. By later week-2 into week-3, while the “usual” 8-1 to 4-5 variations continue, I like the phases 2-3 of the snr 250mb psi plots for both the MJO and GWO. In the longer term, the MJO may again tilt toward octants 3-5 with the GWO displaced toward octants 2-4 of their phase spaces.
Stronger than I would have thought a couple weeks ago (seasonal cycle issues), at least a “preview” of the barrage of western and central
As already offered in past postings and implied above, a rendition of the weather-climate situation similar to the 2007-08 cold season may occur for 2008-09. That suggests more western and central
Intense to severe tropical thunderstorm activity is likely to increase across Africa and the equatorial Indian Ocean ~weeks 1-2, and then expand east and northeast into
The tropical cyclone risk for
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 an increase during the last week.
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, where WB formally introduce the GWO (WB (2008)), has been accepted for publication and resubmitted to MWR. A pdf version (before revision) can be downloaded from the following link:
Hopefully we can get the revised version posted soon.
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! I should be able to do a discussion next weekend, ~11-12 October.