Saturday, October 18, 2008

Atmosphere Spiraling into Recession?

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 Indian Ocean. Anomaly magnitudes are loosely slightly under 0C with totals less than 28C. However, a well defined axis of positive SST anomalies, ~1-2C, extends from the Arabian Sea east-southeast to around New Guinea. Shifting south with the seasonal cycle, the warmest SSTs globally are centered on 0-5S/150-160E, with totals in excess of 30C. Our anomalous horseshoes of SST warmth and coolness continue to radiate from the TNWP and equatorial Dateline regions, respectably, projecting on what some consider being a negative phase of the PDO. Links below provide additional SST details. (note the initial projection) (link 18)

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 Indian Ocean tropical convective forcing, centered ~0/80-90E. Latest three-day averaged OLRA per BMRC have been well under minus 50 W/m**2 for this region of severe tropical rainfall. Tropical cyclones (loosely) have been spinning off across the South Indian Ocean and Arabian Sea. Animations of upper tropospheric daily mean vector wind anomalies show subtropical transition to western Indian Ocean (western Pacific Ocean) anticyclones (cyclones). The WH (2004) MJO measure gives a slightly greater than 1 standard deviation projection in octant 3 of phase space, and a more representative strong 2 sigma Indian Ocean signal leaving the base state in. For various reasons, other flare-ups of intense thunderstorm clusters continue across the global tropics. Phase 3 of the 250mb snr streamfunction composite anomalies done on the WH (2004) measure of the MJO best represents the current tropical circulation.

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 Indonesia. These surges have been stronger than any westerly wind events since at least late May 2008. While monitoring is so critical, I think this pattern will continue for the next few months, possibly longer. I have my reasons for thinking that at least the equatorial central Pacific Ocean SST anomalies are going to respond to the atmosphere (cool). Unless there are any “huge changes”, having periods of constructive and destructive interference, the global circulation may exhibit La-Nina characteristics well into 2009. The intensity is unclear.

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 Eastern Hemisphere tropical convective forcing will shift east to roughly the 29C SST isotherm, meaning ~150-160E depending on the impacts from the current trade wind surge. Per above, there is already a well defined positive anomaly SST perturbation east and north of the tropical forcing. Using the MJO time scale of ~3-4 degrees of longitude shift per day, by ~week 3 rainfall may be particularly intense from Southeast Asia into the west central Pacific Ocean. Hence a loose evolution through a “superposition” shown by the snr composite anomalies for 250mb streamfunction and 2m air temperature for GWO and MJO phases 3-5 appears probable during the ~next 1-3 weeks. This suggests general ridge conditions shifting into the western states and troughs for the central and eastern USA.

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 USA, perhaps including intense winter precipitation and thunderstorms, possibly making travel difficult around Thanksgiving. At this point I will also offer that a December rendition of the global circulation depicted by the GWO phase 3-5 snr 250mb composite streamfunction anomaly plots may increase the probability of anomalous cold focusing on the north central USA.

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 Pacific Ocean westerly wind bursts may start. However, a tilt toward a La-Nina seasonal base state is appearing more probable.

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 Indonesia, Southeast Asia, then into the northwest and west central Pacific Ocean. Tropical cyclones may be left in the wake, particularly the Bay of Bengal ~week-2 then the TNWP (possibly impacting the Philippines) week-3. The southwest Pacific Ocean along the SPCZ may see enhanced convection weeks 3-4. The Western Hemisphere should be relatively quiet weeks 1-2. Hybrids are always a concern in any prone basin, especially in a base state that favors AWB.

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.

Ed Berry


Accudean said...

Great Analogy!!!

The atmosphere is in a "credit crunch" of its own. :>)

Keep up the great work. The GWO and AAM webpages are nearly daily web destinations for me.

Ed Berry said...

Thanks, accudean!