AAM Rally in a Bear Atmosphere

“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.

http://www.cdc.noaa.gov/map/clim/gsdm.composites.shtml

Please see links below for global SST details. Little overall change has occurred during the past week. The anomalously cool SSTs recently observed across much of the North Tropical Atlantic Ocean and portions of the Caribbean may have had a significant contribution from extratropical processes. For instance, cold surges accompanying digging troughs into Europe have plunged well south into the tropics during much of the winter, as have similar surges off the USA east coast. The cold front that accompanied the eastern states snowstorm earlier this week is nearing the north coast of South America as I type.

http://www.wmo.int/pages/prog/wcp/wcasp/enso_update_latest.html

http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html

http://www.pmel.noaa.gov/tao/jsdisplay/

http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18)

http://www.cdc.noaa.gov/map/images/sst/sst.long.time.gif

While displaced toward low AAM in phase space, a large, roughly 3 sigma variation of the WB (2009) measure of the global wind oscillation (GWO) has been occurring since roughly 12 February. This behavior has been the dominant component of the subseasonal weather-climate dynamical system within a well established La-Nina base state. The orbit has involved approximately octants 1-4, having a magnitude similar to those seen during boreal fall 2008. The dynamical processes explained by the GWO have been working to try to bring global westerly wind flow back to normal, somewhat analogous to Le Chatelier’s Principle for chemical equilibrium. However, I also think we are seeing an atmospheric variation analogous to a bear stock market rally, and, unfortunately, Le Chatelier’s principle cannot be applied to the latter.

More specifically, the current GWO orbit in phase space is relatively “clean’, following the chain of events outlined in WB (2009). This dynamical measure of the global circulation also provides some quantitative evidence that the extratropics have been recently forcing the tropics. Broadly, there was first strong poleward AAM transport during the first half of February centered ~35N, followed by a strong positive global frictional torque, then global mountain torque. Please see AAM plots for details. Presumably involving the eddies and mass circulations (on our list to quantify along with real-time diagnostics), downward transport of anomalous subtropical easterlies ramped up the frictional torque. Anomalous high surface pressures then increased the global mountain torque. Through 4 March, global relative AAM tendency is again becoming negative, forcing the GWO toward Octant 1 while orbiting around the La-Nina attractor.

Primarily zonally oriented Rossby wave energy dispersions (RWDs), observed during the past several weeks, linked to these complicated dynamical processes have subsequently impacted the deep tropics. For example, the upper tropospheric anomalous twin subtropical cyclones connected with La-Nina were forced west of the Dateline. Intense zonal mean easterly wind flow anomalies that have been dominating the subtropical atmospheres have also weakened a bit, while shifting poleward. In fact, there is even anomalous zonal mean westerly wind flow across the northern subtropics (~5m/s at 200mb), regionally in the Western Hemisphere.

All of these processes have been trying to “jump start” the atmosphere. Regional scale responses have included progression of the PNA central Pacific Ocean ridge-USA west coast trough pattern, and an amplifying central North Atlantic Ocean ridge (not the NAO; this is a dipole of anomalies). As expected given the GWO orbit, these synoptic evolutions can be seen fairly well from looking at phases 1-4 of the GWO 250mb snr PSI composite anomaly plots.

Consistent with our quasi-stationary La-Nina base state, tropical convective forcing remains loosely focused on Indonesia, centered ~0/120E. Per above, a “poor excuse” of a subtropical jet extends from the Northern Hemisphere twin subtropical cyclone near the Dateline into the USA Desert Southwest (with lots of mid/upper tropospheric cloud cover). At least diurnal convection continues across tropical South America and Africa. Retaining the interannual signal, the WH (2004) measure of the MJO has ~1.5-2 sigma projection in octants 4-5 of phase space. Subtracting out ENSO, the signal is much weaker. In this case, the latter is more realistic (need to understand how to interpret any index; the Rottweiler is always watching!), the MJO signal is negligible. Phases 4-5 of the MJO snr 250mb PSI composite anomaly plots best represent tropical circulation anomalies, as they generally have since boreal fall 2008.

Where does the atmosphere go from here? Unlike the current financial markets, relative AAM may have found a “bottom” for the boreal 2008-09 cold season. This behavior would be consistent with that seen a year ago. As I have already typed in past postings, La-Nina circulation anomalies are likely to linger well into spring (at least), with synoptic variations tied to GWO. Synoptic responses shown by the GWO snr 250mb PSI (and other variables) composite anomaly plots for ~phases 8-1 to 4-5 shifted toward low AAM are probable “until further notice”. These will work with the seasonal cycle. This suggests a preference of more progressive western and central states troughs. However, like the stock market volatility (and different from a year ago), there will be deviations including eastern USA troughs and transient ridges from Hell.

Numerical model performance has suffered significantly during the last several weeks literally due to the GWO. I think their forecasts for the next ~5 days are useable (predictability always decreases during transition seasons). During weeks 2-3, the added subtropical westerly wind flow (per above) may help to extend the East Asian jet (shifted north) into the western USA. That may contribute to more energetic progressive troughs including their expected possible high impact weather. This does include warm sector severe local storms (remembering tropical moisture transports issues through the Gulf of Mexico) and cold sector (thunder) snowstorms with individual baroclinic cyclones. However, drought conditions are probable to continue intensifying across the central and southern High Plains.

I trust the expertise of the appropriate meteorological agencies to alert the public of additional weather hazards worldwide. Notable events continue. Locations centered on Indonesia and working into the Philippines are likely to get hammered with intense-severe tropical thunderstorm activity for at least the next 2-4 weeks. An elevated risk of tropical cyclone activity is probable around the north coast of Australia the next 1-2 weeks.

Appendix

All presentations from the 24 February 2009 GWO workshop are available via anonymous ftp. If you have not received information on how to retrieve these, let me know. There was excellent attendance at this day-long event, and feedback was strongly positive. We appreciate all the support!

Links to CPC and PSD ENSO discussions, and a new experimental forecast technique involving a coupled LIM (3^rd link below):

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

http://www.cdc.noaa.gov/forecasts/clim/

The following are links to information about the stratosphere and other nice monitoring tools:

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

http://code916.gsfc.nasa.gov/Data_services/met/ann_data.html (new stratosphere link!)

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

http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html

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

http://www.wmo.ch/pages/mediacentre/news/index_en.html

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 (2009)), is (still) awaiting publication in MWR. A pdf of an in press version can be downloaded from the following link:

http://www.cdc.noaa.gov/map/clim/wb08_revised_final.pdf

In addition to the subseasonal snr composite anomaly plots, we would like near real-time discussions with “weather maps” to become a routine part of the ESRL/PSD GSDM web site sometime soon. Part-2 of our GWO paper will discuss the latter. 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, and extremely unscientific!

I will attempt to post a discussion the weekend of 14-15 March 2009.

Ed Berry