Sinking Deeper into La-Nina?

“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 being updated daily. There are still some map room issues that will hopefully be resolved soon. WB (2009), 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.

These discussions are part of an experimental effort involving linking weather and climate. We are moving forward on having a one-day workshop in Boulder during about mid-February 2009 on the WB (2009) GWO. Hopefully details will be available next week (22-26 December).

The warmest SSTs globally still extend from northwest of Australia to the Dateline ~10-15S, with totals in excess of 30C and departures from climatology greater than 1C. However, significant cooling of equatorial central and eastern Pacific Ocean SSTs has occurred during the last 1-2 weeks, with nearly minus 1C anomalies across all Nino regions per 5-day averaged TAO buoy data. In fact, SSTs are ~minus 1.5C below normal at 0/160W, and anomalies colder than minus 5C are present at 125m depth/135W. The subsurface equatorial Pacific Ocean anomalies are now very similar to a year ago (steeper than normal thermocline).

Bottom line, this is the type of “Nino SST” response that has been anticipated by us since at least early October, in the presence of the global ocean-land-atmosphere dynamical system exhibiting La-Nina characteristics (with variations) arguably since December 2006. How much additional Nino cooling occurs is unclear; however, “my expectations (in terms of magnitude)” have already been exceeded.

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 wind and convective signals are once again are out of sync for at least the third time since October. Perhaps this is a characteristic for a “second year La-Nina”. Tropical convective forcing is somewhat disorganized, with enhancement focused on central Indonesia into northern Australia, tropical South America and South Africa. The latter is attempting to expand into the southwest Indian Ocean, and there is a strong flare-up over the southern Arabian Sea.

Updated through 18 December, the WH (2004) measure of the MJO shows a ~1.5 sigma projection in octant 7 of phase space; i.e., the west Pacific Ocean. Retaining the interannual and ENSO signals gives literally no projection. The latter is much more reasonable. The "artificial" west Pacific MJO signal is coming from the winds. The dynamics responsible for those winds are more accurately explained and properly represented by the WB (2009) measure of the GWO. I will only summarize below. Please see the AAM and other plots for details.

Since about mid September, with the important exceptions of two large ~3 sigma 20 to 30-day variations of the WB (2009) measure of the GWO, ~10-day orbits tilted toward low AAM have occurred. More generally, if a 90-day averaged location in phase space of the GWO is calculated, there would be a drift towards octants 8-1-2. The November orbit was slower, with a large excursion toward high AAM, and had better interactions with the tropics. There was considerable frictional dissipation of anomalous subtropical westerly wind flow during the November variation linked to extratropical storm track activity especially across the North Pacific Ocean.

In any case, the two large variations loosely involved first poleward AAM fluxes, then positive surface torques and finally interhemispheric positively phased subtropical wavetrains (Branstator (2002); +SWT). These +SWTs have had phase speeds of ~20-25m/s, and aligned by the base state have maintained the upper tropospheric zonally asymmetric wave 0/1 La-Nina distribution of tropical circulation anomalies consisting of twin Indian Ocean (Dateline) anticyclones (cyclones) that has been present since early October.

A strong poleward AAM transport signal (all part of eddy feedback processes from our quasi-stationary La-Nina global circulation state) appeared ~1 December (maximum transport ~40N) leading to a similar chain of events as described above. However, the response of the global surface torques was apparently “damped” suggestive of the current on-going weaker and faster GWO orbit through phases 8-1 to 4-5 then 8-1 behavior. The accompanying +SWT, however, is quite robust with wind speed anomalies ~40-60m/s at 250mb. In fact, with strong poleward AAM flux once again, similar to 2007-08 an interhemispheric positive phase of a Branstator (2002) circumglobal teleconnection meaning anomalous midlatitude ridges is back.

So, sparing anymore “Gone with the Wind”, I think our quasi-stationary La-Nina base state is continuing to mature. While currently just slightly below the R1 data climatology (through 17 December) after the plus 2 sigma November excursion, how low global AAM may drop is unclear. There is nice meridional symmetry of zonal mean zonal wind anomalies featuring equatorial westerlies, strong subtropical easterlies (5-10m/s at 200mb both hemispheres) then westerlies across the higher latitudes. It is probable this La-Nina situation will continue at least well into boreal spring (yes, more and more coupled models have been catching on, and other “organizations” are starting to “yield” a bit).

Responding to increasing regional scale divergence forced by +SWT, tropical convection is probable to increase across the Indian Ocean during the next 1-2 weeks. The details are unclear. However, by early January there should be a large region of intense to severe thunderstorm activity from roughly the equatorial Indian Ocean into Western Australia possibly focused ~5S/90-100E. Perhaps at that time the wind and convective signals will get back in sync, and “stay that way”.

Evolutionary behaviors depicted by phases 8-1-2-3 of the GWO 250mb snr composite psi anomalies are likely to represent the extratropical circulation at least through week-2. USA weather ramifications including the likelihood of additional extreme weather events should be “common knowledge” by now. For reasons, there is a bit of a historical maximum for significant/severe winter storm development to occur on the Plains during early January. We will see if that is the case for January 2009.

Speculating farther into next month, uncertainty increases because of seasonal cycle issues. I am still concerned that at least episodic events of enhanced convection across both the warm southwest Pacific and Indian Ocean/Australian regions may occur simultaneously. The role of MJO activity is uncertain. Bottom line, lack of MJO (additional MJO) variability may suggest a circulation tilt toward that shown by the snr 250mb psi composite anomalies for GWO phases 8-1-2 (3-4-5). On average JFM may see anomalous cold/wet (warmth/dryness) shifted toward the USA west coast into the Northern Plains (Deep Southeast), a slight westward displacement from 2007-08. There would still be an active southwest flow storm track across the Plains, but perhaps locations such as the Dakotas would have an increase of “the classic Great Plains blizzards from days back”. Finally, given recent behaviors, drought conditions (there is a multiyear component) may return to portions of the High Plains especially from west Texas into southwest Kansas.

Internationally, the 3 regions of enhanced tropical rainfall discussed above are likely to continue through week-1, with consolidation probable across the Indian Ocean into Western Australia at least weeks 2-3. Frontal thunderstorm activity may become quite intense across portions of Australia going into January. Regardless of the behavioral details, most of Indonesia and even the Philippines (at times) are likely to experience anomalous rainfall including severe thunderstorms and flooding “until further notice”.

The focus for tropical cyclone development may shift into the South Indian Ocean (TC Billy and Cinda understood) to the northwest coast of Australia during austral summer. In fact, an increase in that region to above climatology is possible during weeks 2-3. I would be surprised not to see at least one or two tropical cyclone developments along the SPCZ east of Australia into the South Pacific Islands during JFM given the very warm ocean temperatures. 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 past 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 (2009)), 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 27-28 December.

Ed Berry