La-Nina Impacts HIGHLY Probable to Continue at Least well into Boreal Spring 2009

“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. Negative SST anomalies across all Nino regions have warmed ~1C during the last few weeks. There has also been some warming at depth along the equatorial ocean thermocline from ~140E to the west coast of South America (per TAO buoy data). However, similar to a year ago, a contribution to the warming may be the annual cycle. Recall during late boreal fall 2008 the Nino SSTs responded to the global circulation that was already exhibiting El-Viejo characteristics. Utilizing Nino 3.4 SSTs including the ONI as a measure of the ENSO situation was unrepresentative at that time, and that may be the case well into Northern Hemisphere spring.

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

The global ocean-land-atmosphere dynamical system is well entrenched in a quasi-stationary La-Nina base state. In fact, and possibly linked to recent tropospheric impacts from the January 2009 major sudden stratospheric warming (SSW), global relative AAM is at the lowest value so far. Updated through 25 February, global relative AAM was ~minus 2.5 standard deviations below the R1 data climatology, similar to a year ago during the strong La-Nina. Put another way, just like the stock market has found a new “bottom”, so has AAM. Conditions in the stratosphere have returned to about normal.

The WB (2009) measure of the GWO during the last 40 days has ~2 sigma displacement toward octants 2-3 of phase space, essentially the La-Nina attractor. Not wanting to get too involved with the details of the current earth-atmosphere AAM budget (see plots), I think there may be another equilibrium "of sorts" of physical processes going on. For instance, the global frictional torque has recently spiked to ~plus 20 Hadleys, with most of that coming from enhanced trades. A portion of the latter may be coming from zonal mean negative AAM anomalies being brought down to the surface via mass circulations (enhancement of the Hadley cell; see earth AAM). In any case, this is an example of the atmosphere trying to get out of La-Nina, analogous to recent stimulus packages attempting to halt economic recession. There has also been an abrupt poleward shift of zonal mean AAM transport from ~35N to 50N, with a weak subtropical source. The latter is not good news for Northern Hemispheric locations experiencing drought.

Observationally, there have been several rapid variations involving zonally oriented Rossby wave energy dispersions (RWDs)/dispersive baroclinic wave packets during the past several weeks. In addition to causing difficulties with global numerical model predictions, these RWDs have also disrupted some of the tropical convective forcing. However, per full disk satellite imagery, enhanced rainfall is consolidating near 0/120-140E, while both tropical South America and Africa remain active. Retaining the interannual signal, through 26 February there is ~2 sigma MJO projection in octant 4 of WH (2004) phase space. However, in reality, there is no physically significant MJO variation of tropical convective forcing currently going on (past rogue MJO understood!).

Interhemispheric meridional symmetry of zonal mean zonal wind anomalies is well pronounced, including easterlies across the subtropical atmospheres. For the first time in at least a few weeks, the upper tropospheric zonal asymmetric portion of tropical circulation anomalies has returned. There are well defined twin cyclones near the Dateline (~30-40m/s anomalies at 150mb) with weaker anticyclones across the Indian Ocean. Anomalous midlatitude ridges continue to dominate the extratropics.

A loose superposition of phases 2-4 of both the GWO and MJO snr 250mb psi composite anomaly plots best depict the current global circulation. This type of circulation is probable to persist well into March, and possibly most of this upcoming spring. Because of on-going feedback processes not discussed, phase 5 of the MJO snr OLR composite anomaly plots may best represent the current tropical forcing, and, on average, may continue “until further notice”. The latter has generally been the case for the past 90 days.

Regardless of the details, little change in the overall synoptic pattern across the PNA sector is likely for at least the next several weeks. The La-Nina (and ENSO variations in general) characteristics of a global circulation “suddenly do not just go away (for reasons; insert angry Rottweiler!)”. There will be variations with the seasonal cycle, including shortening wavelengths that could lead to deep troughs across the central USA states (for example). More generally, on average, the outcome of temperature and precipitation anomalies for the lower 48 states during March-June 2009 may have some similarities to that same period during 2008. However, unlike 2008, subseasonal activity this boreal winter has been much weaker. While that could change, compared to a year ago, I am concerned that an outcome for boreal spring 2009 that is more consistent with the La-Nina composite signal may occur. This includes intensifying drought with anomalous warmth across the central and southern High Plains into Texas, possibly spreading northeast (see the U.S. Drought Monitor for other areas).

I trust the expertise of the appropriate meteorological agencies to alert the public of additional weather hazards worldwide. There have been some recent notable events, including extremely active weather from portions of the Mediterranean Sea into the Middle East. The latter may continue for at least another couple of weeks. Locations centered on Indonesia are likely to get hammered with intense-severe tropical thunderstorm activity for at least the next couple of 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 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 6-8 March 2009.

Ed Berry