Wrong Turn in the REAL 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

The 91-day signal to noise ratio (snr) anomaly composites are now updated daily, centered on the date shown. Please see product descriptions. WB (2008), part-1 of a 2 part paper where the GWO is formally introduced, is in press for MWR publication. There is a link in the Appendix to download the manuscript.

The warmest SSTs globally persist ~140E within 20 degrees of the equator having totals ~29-30C but with weak anomalies. Larger positive anomalies ~1-2C are in the region of the equatorial Indian Ocean with totals near 29C. A strong equatorial trade wind surge (~10m/s anomalies) continues from ~140E to east of the Dateline. There is upwelling of the oceanic thermocline east of the Dateline, leading to roughly negative 2-3C subsurface anomalies ~100-200m depth along the equator per latest 5-day averaged TAO buoy data. Remember that these anomalies are in the presence of annual cycle cooling. SST anomalies ~minus 1-2C are also present from about 160E-140W within 10 degrees of the equator.

Bottom line, I think we may be waiting for the tropical Pacific Ocean “SSTs to really kick in” responding to the global circulation already having La-Nina characteristics. In fact, speculating, are we starting an evolution of another SST cold event which may mature as late as 2009-10 that will even make the Nino 3.4 people happy? See links below.

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

I would like to keep this discussion relatively brief. The subseasonal behaviors of several components involving the earth-atmosphere-land dynamical system have not played out as I expected during the last few weeks. However, what has occurred does not surprise me. Regardless, this is an example of why rigorous daily monitoring within the WB (2007) GSDM framework is critical, and relying on the numerical models (multi model ensembles) alone is scientifically unrealistic and indefensible. Furthermore, empirical techniques employed by some synopticians to track baroclinic signals on Hovmoller diagrams as a predictive tool many weeks in advance also has little scientific merit.

Eastern Hemisphere tropical convective forcing has been shifting west during the last week or so, and is currently focused around 5N/100E. Intense to severe tropical thunderstorm activity extends from near 60E to western Indonesia and covers most of the Bay of Bengal, including a tropical cyclone about to impact India. The latter is approximately 35 days after the last period of enhanced rainfall in that region, and it is possible a MJO component may evolve. Leaving the interannual signal in, there is about a 2 sigma projection in octants 3-4 of WH (2004) phase space. A faster signal tied to the WB (2008) measure of the GWO has led to some convective enhancement across the Western Hemisphere. The recent flooding rainfall across the USA Pacific Northwest is attributable to an “atmospheric river” of moisture transport from the Eastern Hemisphere tropical convection.

Phase 4 of the WH (2004) MJO snr 250mb composite psi anomaly plots reasonably depicts the current tropical circulation. In fact, per animations of upper tropospheric daily mean vector wind anomalies, the spatial pattern of Indian Ocean anticyclones and west Pacific cyclones is similar to a couple of weeks ago. The notion offered that the opposite sense to this phase would not be as robust was correct.

So, what happened? Obviously not the coherent eastward shift of tropical forcing/circulation behavior from the Eastern into the Western Hemispheres I discussed was likely in my last several postings. Nevertheless, I do feel there is a scientifically defensible attribution, and this will be one of the many foci of WB during the next several weeks. I think dynamical processes explained by the WB (2008) measure of the GWO contributed, starting with the ~3 sigma orbit in octant 4 of phase space during mid October. Poleward AAM transports and surface torques created a large tendency working to increase zonal mean westerly wind flow in the subtropical atmospheres.

Cutting to the chase, it is possible Rossby wave energy dispersions (RWDs) linking the tropics and extratropics (fast GWO) worked to oppose this tendency, wanting to retain the global circulation in “La-Nina”. Specifically, and beyond the scope of this discussion, the latter is in reference to complex dynamics working to reduce global westerly wind flow, best represented synoptically by ~phase 3 of the WB (2008) GWO 250mb snr composite psi anomaly plots. That is, a positive phase of the Branstator (2002) circumglobal teleconnection of anomalous midlatitude ridges, observed during the boreal winter of 2007-08. Please remember that I am talking about forcing-response-feedback relationships and the not the unrealistic notions of equilibrium states (ex., Charney and DeVore 1979).

Currently, and loosely similar to about a month ago, there is an interhemispheric signal of poleward AAM flux, ~45N and 50S. The global surface torques is positive including a ~20 Hadley East Asian mountain torque (see AAM plots for details). A synoptic response has been for a cold outbreak off the coast of China and an expanded North Pacific Ocean jet. This is an example of a situation when the jet “outruns” the Eastern Hemisphere tropical convective forcing. Phases 4-5 of the WB (2008) GWO snr 250mb composite psi anomaly plots best depict the extratropics, and should through at least week-1.

What road the atmosphere takes from here is extremely uncertain, particularly for timing and details. Statements such as forecaster confidence of something like 4 on a scale 1-5 for a USA week-2 prediction of temperature and precipitation anomalies are unrealistic. The numerical models have been inconsistent, to say the least, for the last 1-2 weeks. The tropics and extratropics are still out of sync.

That said, what appears most probable is for a GWO 8-1 transition ~weeks 2-3 per above, then perhaps coupling of the tropics and extratropics across the Eastern Hemisphere weeks 3-4.That is, possibly a superposition of the circulation states shown by the GWO/MJO phases 3-5 of the snr 250mb composite psi anomaly plots during the first half of December. Given base state issues briefly discussed above, I do feel confident that the La-Nina side of phase space is the most probable “until further notice”.

Weather ramifications include above (below) average temperatures returning to the eastern (western) USA during roughly week-2/3 along with an active southwest flow storm track on the Plains. Much of the west coast could receive generous precipitation. Anomalous cold may then focus on the central states afterward. Interestingly, what may actually occur is ~1-2 week delay of the outlook statements offered in past postings. Monitoring is critical, including the future of the Eastern Hemisphere tropical forcing, which will impact the USA. The risk of extreme weather events (ex., blizzard conditions and severe thunderstorms) affecting large portions of the country, including having adverse impacts on Thanksgiving and even Christmas travel, is possible to be elevated the next several weeks.

It is unclear if and when the above mentioned tropical forcing will coherently shift east. However, locations from the west central into the Southwest Pacific Ocean are probable to be at risk from severe rainfall and cyclones ~weeks 2-4 (week-1 understood). Generally climatological precipitation should continue for tropical South America and Africa the next several weeks. It is not out of the realm of possibilities to see multiple regions of enhanced tropical convection during the next several weeks, but with a focus shifted toward the Indian Ocean and Indonesia ~100-120E (as part of what may be an emerging quasi-stationary component of a La-Nina base state).

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.

Appendix

Links to CPC and PSD ENSO discussions:

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

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

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

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

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 (2008)), has been accepted for publication MWR. A pdf of the 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 hope near real-time discussions with “weather maps” will 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! I plan on posting a discussion the weekend of 22-23 November.

Ed Berry