Friday, March 27, 2009

The GWO Giveth then Taketh Away?

“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.

Please see links below for global SST details. SSTs have been slowly warming across the convectively suppressed southwest into the central equatorial Indian Ocean. Anomalies are roughly plus 1-2C with totals approaching 30C. However, the South Indian Ocean remains anomalously cool on both sides of Australia into portions of central Indonesia. The former are the warmest I have observed “in a while”, and may signal the onset of enhancement of tropical convective forcing during the next few weeks (more said below). Finally, the Nino SSTs remain a bit cooler than normal and weak-moderate subsurface anomalies (~1-3C; see TAO buoy data) still suggest a steeper than normal equatorial thermocline. (note the initial projection) (link 19)

Sounding like the proverbial broken record during this 2008-09 La-Nina from Hell, the weather-climate situation is an extremely complicated mess, with lots of “tugs and pulls”. However, only from rigorous daily monitoring including evaluation of our “GWO-based diagnostic tools”, I do feel fairly comfortable with my interpretation. In the following, I again want to broad-brush, particularly since many readers are getting used to studying the budget terms of the on-line AAM plots, as well as the WB (2009) measure of the GWO.

Since October 2008, there have been “regular” ~25-30 day variations of the GWO, with each orbit spiraling toward the La-Nina attractor in phase space. This is a significant difference from the 2007-08 La-Nina, when slower subseasonal activity including MJOs occurred. Perhaps similar to the bear financial markets, the depths of El-Viejo were reached during late January and mid-late February. The latter were roughly 2-3 standard deviations below the R1 data climatology (the major SSW contributed; see past discussions), comparable to the strong “season of the witch” 2007-08 cold event. One direct response was for drought to intensify across many portions USA including the central and southern High Plains, while locations across the northern portion of country received significant to excessive precipitation.

Starting late February, dynamical processes explained by the GWO including meridional eddy momentum transports and the surface torques have worked hard to increase global westerly wind flow. Much of that contribution has been in the equatorial and Northern Hemisphere subtropical atmosphere, where upper tropospheric zonal mean westerly wind flow anomalies were ~5 m/s. Zonally oriented fast Rossby wave energy dispersions (RWDs)/subtropical baroclinic wave trains (SWT) involved with the GWO literally forced Indonesian convection into the anomalously warm southwest Pacific Ocean (SWP) by the middle of this month. I did not expect the latter (Rottweiler is very angry with me!). In any case, that was good news for many dry portions of the country.

The SWP forcing also did its part to add additional westerly wind flow to the global and various zonal mean bands of the atmosphere (including substantially decreasing intense subtropical zonal mean easterly wind flows). In fact, there was even a weak surface westerly wind event mostly south of equator having anomalies ~10m/s. Should this same type of behavior occur in May (for instance) across the west central Pacific Ocean on the equator, maybe this will be the start of an “exorcism”. Right now, in terms of the possibility of a warm event, I am not optimistic about that option. Through 24 March global relative AAM is only slightly below the R1 data climatology. Similar to what some may ask about the current bear market rally, is this AAM rally about to end?

Eastern Hemisphere tropical convective forcing has become incoherent. A “GWO-driven” MJO signal is moving through the Western Hemisphere. Just like that observed December 2008, this “MJO” evolved in the region of Indonesia, inconsistent with past documented work. That is why the WH (2004) measure of the MJO indicates ~1.5 sigma projection on octant 8 of phase space, updated through 26 March (ENSO removed). I do expect this signal to return to the Eastern Hemisphere during the next couple of weeks, and I think it is plausible to see some enhancement initially over the anomalously warm waters of the Indian Ocean (areas cited above).

Zonal mean subtropical easterly wind flow anomalies are starting to increase, and global relative AAM tendency has already become negative. As convection gets reestablished across the Indonesian region ~weeks 2-4, global relative AAM may decrease to at least 1 sigma below normal suggesting a re-loading of La-Nina (subseasonal perspective). However, seasonal cycle issues may also have an impact, and I do think we have seen the AAM bottom for this boreal cold season. Repeating from my last posting, we need to carefully monitor Southern Hemisphere zonal mean zonal wind anomalies this upcoming austral winter for ENSO insights.

The GWO is probable to do at least one circuit shifted toward octants 8-1-2 during the next 1-3 weeks. The corresponding GWO snr 250mb psi composite anomaly plots may best represent the global circulation the next few weeks. At some point GWO snr phase 3 (La-Nina base state) may return, meaning a positive phase of a Branstator (2002) circumglobal teleconnection favoring anomalous midlatitude ridges. The latter would not be good news to dampening many of the drought areas. Phases 4-5 of the MJO snr 250mb psi composite anomaly plots should loosely depict tropical circulation anomalies for the next few weeks. Obviously, phase 8 currently does not, which “tells you something” about calling the Western Hemisphere tropical convective dynamical signal (per velocity potential plots) a “MJO”.

More troughs are probable to impact the western and central USA during the next couple of weeks. While there will be a tendency for them to be progressive, I would not be surprised to see at least one more synoptic event similar (not the same weather) to the system currently pounding much of southwest Kansas with a blizzard as I write. At some point (perhaps late week 2/week-3) troughs may again dig off the west coast before shifting inland (trough-ridge-trough pattern for a period). Weather ramifications are understood, including internationally.


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 (3rd link below):

The following are links to information about the stratosphere and other nice monitoring tools: (new stratosphere link!)

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

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

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. An early on-line release can be downloaded from the following link:

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, extremely unscientific, and makes the Rottweiler VERY angry! I am planning on posting a discussion next weekend, 3-5 April.

Ed Berry


DougMitchellChaser said...
This comment has been removed by the author.
DougMitchellChaser said...

You sound like what renowned expert meteorologist Kevin Martin from SCWXA said. He predicted a couple years ago of an El Nino returning this next year, possibly even the year after that. Also his UJEAS program shows April being a relief for Southern California.

He was the sole predictor of the SOuthwest Arctic blast in December 2008 with the UJEAS program as well.


Ed Berry said...

Hello Doug,

Thank you for the comment. Hope you find my latest post useful.


Bill said...

Hi Ed,

I was linked here from another website.

I'm not sure but your models are somewhat similar to some material I have been doing on an amateur basis for the ENSO (very simple version of course).

I had noticed the Trade Wind correlation before and was looking for something bigger than the SOI to be the driver. I saw someone posting about Atmospheric Angular Momentum and thought, ah, this could be it. Seemed to work.

Let me know if I should drop this idea or not.


Ed Berry said...

Hi Bill,

You have the correct idea. As you say, it is a "simple" viewpoint. Low AAM regimes are generally characterized by strong trades (contribute to positive frictional torques), and the latter can lead to cooling of the Nino SSTs. However, please remember that the AAM component of the GWO, as well as the GWO itself, is a global dynamical measure of the circulation.

ONI is a regional univariate SST measure, and as was the case for 2008-09, the GWO led ONI. I do not agree with using ONI as a measure for ENSO. Please see some of my past discussions.

Hope this is useful,