“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. Part-1 of WB (2008), where the GWO is formally introduced, is in press for publication in MWR. Please see link in Appendix.
Responding to anomalous convection, SSTs have cooled across portions of the equatorial
http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)
Weather-climate signals have become significant, and the global circulation has evolved to exhibiting a strong La-Nina behavior. I can only give a few dynamical reasons in the interest of brevity. First, I will address this situation from the “GWO perspective”, and then bring in the roles of the tropical convective forcing.
From an AAM budget viewpoint, there apparently exists a balance of forces wanting to add and remove global and zonal mean wind flow anomalies in what may become a quasi-stationary La-Nina situation. For instance, around 25S and 30N zonal mean negative AAM anomalies approaching 2 atmospheric momentum units (AMUs; through 16 October) flanked by somewhat weaker positive anomalies on their poleward flanks are present. This means there are poleward shifted zonal mean jets in both hemispheres in a circulation base state favorable of anomalous midlatitude ridges and anticyclonic wave breaking (AWB) baroclinic development.
When viewing animations of daily mean upper tropospheric vector wind anomalies, for at least the past week the synoptic eddies have generally been NE-SW (NW-SE Southern Hemisphere) tilted. This orientation has been favorable for fluxing AAM out of the subtropical into the midlatitude atmospheres. First across the Southern Hemisphere earlier this month and then over the Northern Hemisphere during the last 7-10 days, zonal mean subtropical AAM sinks and midlatitude sources have been well pronounced. Finally, having a global signal of ~plus 10 Hadleys, a well defined interhemispheric dipole of positive (negative) zonal mean frictional torque in the subtropical (midlatitude) atmospheres has been present for at least the past 10 days. The latter suggests anomalous surface easterlies in the subtropics with frictional dissipation in the storm track regions.
Overall, global relative AAM minus the QBO signal may have (for now) reached an equilibrium of ~1 standard deviation below the R1 data climatology due to offsetting dynamical feedback processes trying to keep the atmosphere rotating at the same rate as the earth. The combination of the surface torques and AAM transports has spiked the calculated tendency to ~plus 30 Hadleys. The computed AAM tendency, one of the components of the WB (2008) measure of the GWO, has peaked to ~plus 40 Hadleys. However, there may be some averaging issues for the latter. In any case, the GWO has orbited to at least a 2 sigma projection in octant 4 of phase space. I do think we are seeing another fast GWO variation involving phases 4-5 and 8-1, in the presence of the phase vector orbiting around octant 3 (La-Nina).
Phase 3 of the WB (2008) GWO 250mb snr streamfunction composite anomaly plots best represents the global atmosphere. Similar to what was often observed during JFM 2008, remarkable for October, there is currently a strong positive phase of the Branstator (2002) circumglobal teleconnection. The latter includes my familiar statement of interhemispheric meridional symmetry of zonally symmetric zonal mean zonal wind flow anomalies.
Full disk satellite imagery and other tools show strong
Summarizing, with tropical-extratropical coupling, the GWO is still “calling the shots” and the MJO component is “going along for the ride”. Rossby wave energy dispersions (RWDs) continue to be zonally oriented, suggestive of dynamical processes involving the mountains (not discussed today) and AAM transports. Part of the positive global frictional torque is due to a strong trade wind surge (~10m/s anomalies) from the equatorial Dateline to roughly
Worth repeating from my last posting, regardless of what happens, any statement about the outcome of the 2008-09 boreal cold season must consider roles of subseasonal variability and global tropical SSTs. “ENSO neutral” is a completely inaccurate description about the current weather-climate situation, and may be “until further notice”.
Like a week ago, I feel fairly confident where atmosphere will go during the next several weeks, and there is little change in my thinking. My feeling is that the
I also think another “GWO/MJO 7-8-1” transition depicted by the snr plots roughly weeks 4-5 may be in the offing. Again, timing is white noise. Per above, it is looking more probable that should this kind of transition occur, it will be a perturbation that destructively interferes with a La-Nina base state. Weather ramifications may include a stormy period focusing on the western and central
The same issues for this boreal winter remain, and "outlooks/speculations" per my past discussions are unchanged. The anomalously warm west central Pacific Ocean always may be the “bail out” from keeping the global atmosphere spiraling “too low (AAM)” in GWO phase space. Our nemesis of 2 regions of tropical convective forcing may return, and/or episodic intense equatorial west
Internationally, during the next 1-3 weeks, per above, intense to severe tropical thunderstorm activity is probable to shift east-northeast from the central Indian Ocean through
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.
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. The first of a two-part paper, where WB formally introduce the GWO (WB (2008)), has been accepted for publication MWR. A pdf of the in press 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 ESRL/PSD GSDM web site 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! My next complete discussion is not likely until around the weekend of 31 October, 1-2 November. I may be able to post a short update ~24 October.