The Devil Deals the Atmosphere; PNA Retrogression or Bust!!!

“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 map room issues that are being worked on. 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 a component of an experimental effort involving linking weather and climate. The formal announcement for the 24 February 2009 one-day (~9am-5pm MST) workshop on the WB (2009) GWO has been released through various mailing lists. If you have not received this, please leave a comment with your email address, and I will forward. Hopefully we can place this information on the above GSDM web link ASAP.

The general spatial pattern of global SSTs and their anomalies persist (see links). Tied to recent variations of atmospheric and tropical forcing (more said below), a slight lessening of the cool Nino anomalies has occurred during the past week (~minus 1-2C per 5-day averaged TAO buoy data). In fact, there is a downwelling oceanic Kelvin wave ~100-200m deep crossing the Dateline. The very warm waters of the Southwest Pacific Ocean have cooled substantially with totals generally less than 30C.

In any case, in terms of the global ocean-land-atmosphere dynamical system, La-Nina is well established. The expected re-emergence became notable by about October 2008, atypical timing based on our limited sample size. Consistent with “encores”, our on-going La-Nina is weaker (but more robust than earlier anticipated by myself) than a year ago (per GWO, MEI, SSTs, etc.).

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

During the past 1-2 weeks the wind and convective signals did reasonably get back into sync. The result has been a perturbation destructively interfering with La-Nina. Behaviors similar to this were observed relatively frequently during the strong 2007-08 cold event. Unlike a year ago, however, the quasi-stationary component of the global circulation has been the most dominate.

In my last posting (3 January 2009; 38^th anniversary of the Great Plains Blizzard for those who remember!), I stated “there is no coherent MJO”. While not entirely inaccurate, I did underestimate what stochastic forcing represented by the WB (2009) measure of the GWO can do.

Recalling the rapid eastward flows of wave energy through the Eastern Hemisphere subtropical atmospheres per past postings, to keep things “short/simple”, I hypothesize that the seasonal/annual cycle became involved. In other words, the flow of wave energy forced tropical convection to propagate east-southeast into the warm southwest Pacific Ocean. The result was a fading in of a weak MJO signal. As I type, upper tropospheric cross-equatorial divergent outflow from this tropical forcing is leading to an extension of the East Asian jet (discussed below). The astute reader will recall discussions of this possibility were previously given. Yes, a real-time web site with maps and figures would help show these kind of behaviors!!!

Full disk satellite imagery and other tools illustrate a large region of intense to severe tropical rainfall centered ~10S/140E extending from Indonesia to the South Pacific islands. There is evidence some separation is occurring, with one region starting to focus on Indonesia and other ~15S/170E. If there is still any MJO signal, the latter region of enhanced convection would be part of it. Updated through 9 January, per WH (2004) MJO measure retaining ENSO, there was ~1 sigma projection in octant 5 of phase space. Regardless, I do think the Eastern Hemisphere tropical forcing will be dominant during the next several weeks.

In spite of the large global AAM tendency observed late December (calculated tendency ~plus 25 Hadleys), global relative AAM has remained below the R1 data climatology (through 8 January). That tells us the La-Nina base state is “holding” (for reasons). Forcing this large tendency included indirect contributions from zonal mean AAM flux convergence ~35N (with some interhemispheric symmetry) due to the midlatitude baroclinic eddies, and north-south mountains. Perhaps responding to complicated extratropical feedbacks from the South Pacific Ocean tropical forcing (ex., Rossby wave energy dispersions (RWDs) arcing through the North Atlantic Ocean; need maps to show!), even though the global mountain torque signal is decreasing, the East Asian component is ~plus 30 Hadleys. These processes are working to extend the East Asian jet (with an accompanying strong cold outbreak) which will amplify the evil ridge from Hell just off the North American coast next week; a.k.a. the positive phase of the PNA.

Cutting to the chase, I expect to see constructive interference involving various dynamical processes reloading La-Nina during the next several weeks. Many of the components are captured by the WB (2009) measure of the GWO. I am optimistic that the wind and convective signals will remain coupled.

Animations of upper tropospheric daily mean vector wind anomalies present a “distorted” and perturbed configuration of the La-Nina zonally asymmetric spatial pattern for the tropical circulation observed since at least October 2008. There are loose twin anticyclones centered on the Indian Ocean but the cyclones have shifted to 150W. However, divergence is also increasing across the Indian Ocean. I do think by later week-2 into week-3 much of the Indian Ocean into Australia and Indonesia will be strongly active, especially south of the equator. Hence it is likely the twin tropical cyclones will redevelop west of the Dateline.

Global relative AAM tendency is already becoming weakly negative. While there will be variations, that negative tendency may become quite large perhaps forcing AAM to ~2 sigma below the R1 data climatology later this month. Supportive of this notion is zonal mean easterly wind flow anomalies are returning to the subtropical atmospheres, and AAM is starting to flux poleward.

The GWO is slowly completing its 4^th orbit in phase space during the last 90 days. While there is currently little projection, per above a shift into octants 8-1 while settling into 2-3 of phase space is probable. The latter has been the 90-day trend, meaning a drift toward the La-Nina attractor. Phase 5 for both the MJO and GWO 250mb snr psi composite anomaly plots loosely depict the current tropical and extratropical circulations, respectively. Phases 8-1 then 2-3 of these plots are the most probable to depict the global circulation weeks 2-4. Synoptically, albeit apparently “delayed” by ~5-10 days (timing always has a noise contribution!), the wicked ridge of the west is likely to discontinuously retrograde perhaps to ~150-160W going into February. That would admit troughs into the western and central USA. During the last few days, week-2 numerical ensembles have been starting to latch-on to this proposed forecast solution.

One of the numerous issues not discussed is that the Northern Hemisphere polar vortex is currently retracted. As the Eastern Hemisphere tropical forcing intensifies, the polar vortex is likely to expand across central and east Asia. However, if not, the East Asian jet may retract so much such that troughs may eventually dig into the Gulf of Alaska ending any possible cold situation across USA. That almost did occur roughly 10 days ago. Having my reasons, I do not think a situation like the 1975-76 USA winter is likely.

Weather impacts per above across the country are already well known. Forced by the oncoming transient +PNA, models have been correctly predicting an Arctic outbreak initially focused Upper Mississippi Valley/Great Lakes starting early next week. That cold air will spread into the eastern states. Care must be taken not to underestimate the ramifications of this airmass given its source. Temperature and precipitation anomalies having similarities to much of December 2008 may then revisit the lower 48 states after ~20 January and persist well into February. That includes the most probable high impact weather from that type of regime.

Dryness is becoming an increasing concern for locations such as California and the southern/central High Plains. As the retrogression occurs starting week-2, it is quite possible the expanded North Pacific Ocean jet will impact most the USA west coast with welcome precipitation for California.

Intense to severe tropical thunderstorm activity will remain generally persistent from Indonesia into the northern Australia for at least the next several weeks. While the South Pacific Ocean will continue to be the “wild card”, some lessening of thunderstorm activity should occur week-1. Much of tropical South America and South Africa may become anomalously active week-1 and perhaps continue week-2. Per above, later week-2 and possibly well into February much of the central and eastern Indian Ocean through Indonesia and Australia may have significant convective enhancement, linked to our quasi-stationary La-Nina regime. I trust the expertise of the appropriate meteorological agencies to alert the public of additional weather hazards worldwide (ex., recent cold in Europe) including official statements for tropical cyclones (ex., Dondo) that are likely to impact regions such as around Australia and Madagascar during the next several weeks.

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 at least an abbreviated discussion on 17 January 2009.

Ed Berry