Saturday, November 29, 2008

La-Nina Roper-Doping the Models???

Please keep in mind the ESRL/PSD GSDM web link, below, while reading this discussion.

The 91-day signal to noise ratio (snr) anomaly composites are currently centered on 23 November due to technical issues. There are also numerous other delayed real-time products such as the AAM plots and vector wind animations. We hope these problems will be resolved soon. WB (2009; likely not to be published until next year), part-1 of a 2 part paper where the GWO is formally introduced, is in press for MWR publication.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.

Please remember that these discussions are part of an experimental effort involving linking weather and climate. Until this work is formalized at the national level, many important scientific issues we are easily well aware of cannot be addressed. Stated another way, it is nearly impossible for me to talk about “everything” in these postings, including offering attribution to unpredictable noise. Also, plans are moving forward to have a one-day workshop on the WB (2009) GWO concepts during February 2009 in Boulder. Stay tuned for details.

There is little overall change in the spatial pattern of global SSTs. The warmest waters extend from north of Australia to near New Guinea, with totals ~30C and anomalies roughly plus 2C. SSTs 28-29.5C covers much of the TNWP southeast of the Philippines and portions of the Indian Ocean. Negative daily mean SSTAs ~1-2C (28 Nov 2008) persist within 5 degrees of the equator from about 140E to 140W, where trades have been strongly enhanced since at least early October.

How much additional SST cooling that occurs in all Nino regions is unclear. However, there has been a decided tilt toward La-Nina for at least the last 3-4 weeks, responding to a global circulation (interacting with the global oceans and land masses) that has been exhibiting those same characteristics arguably since boreal spring 2007. (note the initial projection) (link 18)

There is no change from the scientific matters discussed in my long 22 November 2008 “treatise”. Lack of up to date AAM/GWO and related plots will also limit this writing.

Tropical convective forcing has shifted east to ~0/130-140E essentially covering most of Indonesia into northern Australia. Strong suppression exists across both the equatorial Indian Ocean and west central Pacific regions. About a month ago I wrote that the former should be enhanced at this time, which is an example of what unpredictable noise does to an outlook (more said below). In any event, this spatial pattern of Eastern Hemisphere tropical forcing is consistent with a La-Nina situation.

Intense to severe thunderstorm activity across tropical South America has resulted in deadly flooding conditions across southern Brasil during the past week. Rainfall has also been increasing across South Africa.

While there is a MJO component to the Eastern Hemisphere tropical forcing, ~1.5sigma projection in octant 6 (weaker projection in octant 5 leaving the base state in) of WH (2004) phase space, the wind signal continues to dominate. The enhanced Western Hemisphere tropical forcing is a direct response. There is still a lack of good coupling between the wind and convective signals.

In fact, reconstructed Hovmollers utilizing the WH (2004) RMMs show generally greater than 10m/s westerly wind flow anomalies at 200mb across the Western Hemisphere within 15 degrees of the equator. These same anomalous westerlies are coming back into the Indian Ocean, contributing to the convective suppression. Further, zonal mean westerly wind anomalies at 200mb across the tropical and subtropical atmospheres are ~5-10m/s, largest at 30N and 25S. There is evidence that this anomalous westerly wind flow is starting to propagate poleward into both Hemispheres.

If updated, I suspect that global relative AAM is still a good standard deviation above the R1 data climatology, and that the AAM tendency signal will not be that strong. In other words, the WB (2009) measure of the GWO may be undergoing a fast variation (looping) in octants 7-8-1 of phase space. The extended North Pacific jet/split flow situation this past week across North America was one synoptic response (giving California heavy precipitation).

Directly linked to the Eastern Hemisphere tropical forcing per above, I believe that a meridionally oriented Rossby wave energy dispersion (RWD) is arcing across the PNA sector (animations not updated). This is likely the signal that all numerical models have been playing catch-up to for the last several days. A synoptic response will be a discontinuous retrogression of the wicked ridge of the west from Hell currently just off the USA west coast to ~140W by the middle of next week.

For the past 5-6 weeks I have offered the notion of some form of an 8-1 transition in WB (2009) GWO phase space followed by a December cold regime focused on the middle of the USA. Within the envelope of probabilistic statements, this notion appears to be on track. However, the details of getting here that I have served up have been “anything but”. I do not “conveniently forget” a synoptic evolution suggested 5-6 weeks ago that did not work out. My timing was off by 1-2 weeks, for starters. Additionally, while retrogression of the west coast ridge was expected per above, I did not think that would be a response to "lingering" Indonesian tropical convective forcing.

This only reminds us of the enormous work that is always needed involving linking weather and climate, especially when dealing with red noise dynamical processes represented by the WB (2009) measure of the GWO. These forecast "busts" also offers opportunities to learn. However, I do emphasize these are probabilistic statements, and synoptic notions are presented “to communicate” the best information possible to weather sensitive users. These blog discussions are not very efficient to optimize weather-climate “insights” that can be given by the WB (2007, 2009) dynamical framework (ex., subseasonal “maps” and plume diagrams with real-time live discussions would be far more effective).

I suspect during the next 1-2 weeks the Western Hemisphere wind signal, explained by the WB (2009) measure of the GWO, will come back into the Eastern Hemisphere and excite intense tropical convection across the Indian Ocean. This is likely to initially appear across South Africa, and then shift east. A portion of the Indonesian enhanced rainfall is probable to shift into the warm southwest Pacific Ocean along a westward shifted SPCZ. By roughly weeks 3-4 much of the Indian Ocean into Indonesia ~80-120E should be strongly convectively enhanced. Perhaps there will be better coupling of both the wind and convective signals, within our quasi-stationary La-Nina base state.

An evolution shown by phases 8-1 of the GWO 250mb snr streamfunction composite anomaly plots is likely week-1. That translates to the discontinuous retrogression discussed above of the west coast ridge leading to trough amplification across the Rockies and Plains. Understanding tropical moisture transport through the Gulf of Mexico may be limited; a significant winter storm focusing on the Mississippi Valley must be a concern for the middle of next week (developing event currently across central and eastern USA understood). The coldest airmass to penetrate the lower 48 states so far this new winter season is also likely.

As the tropical forcing returns to the Indian Ocean, AAM will likely decrease to (well?) below the R1 data climatology and may be accompanied by a large negative AAM tendency. The zonal asymmetry of tropical circulation anomalies having Indian (west Pacific) Ocean twin upper tropospheric anticyclones (cyclones) will become enhanced. A strong zonal mean signal of anomalous subtropical easterly wind flow may also return, increasing the odds of another positive phase of the Branstator (2002) circumglobal teleconnection of anomalous midlatitude ridges and anticyclonic wave breaking troughs.

Regardless of the details, I do think it is probable to have a global circulation best represented by ~phases 2-4 of the GWO and MJO 250mb snr composite psi anomaly plots by the latter half of December. Synoptically across the PNA sector, this suggests a continued westward shift of extratropical circulation anomalies with the ridge perhaps to ~150W and troughs initially impacting the USA west coast. The latter should bring welcome precipitation to hopefully most of the west coast (be patient out there – good things come to people who wait!). Impacts from fast GWO variations are unclear. What is also unclear are the circulation anomalies for JFM; however, a rendition of what was observed during boreal winter 2007-08 with added subtropical westerly wind flow may be an option.

In general, USA weather ramifications were discussed in my last posting. Numerical models are going to continue to struggle in this kind of regime having tropical forcing returning to the Indian Ocean (on the list of work for WB to objectively show). I think there is an increased risk of high impact weather of many types during most of next month, and models may not catch them until “the last minute”. With variations, the emphasis may be on the western 2/3rds of the country especially weeks 3-4 (not suggesting the East Coast will be “quiet”).

Internationally, intense to severe rainfall is likely to continue across much of tropical South America including Brasil week-1 shifting into South Africa by week-2. Enhancement of thunderstorm activity is also likely at least week-1 across the southwest Pacific Ocean islands. Per above, moist convection may become less enhanced across Indonesia and northern Australia week-1 in favor of intensification back to the west across the Indian Ocean by week-3. There may be a focus of tropical convection ~100-120E during the latter half of December into January 2009 (while shifting into the Southern Hemisphere). Again, the warm southwest Pacific Ocean may become the “wild card” this boreal cold season.

Please see the latest official tropical cyclone forecasts for all basins. Currently that risk is unclear. I trust the expertise of the appropriate meteorological centers to alert the public of additional weather hazards worldwide. For instance, more strong troughs are digging into western Europe.


Links to CPC and PSD ENSO discussions:

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

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)), has been accepted for publication MWR. A pdf of the in press version can be downloaded from the following link:

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 6-7 December.

Ed Berry


snoman said...

Hi Ed,

Do have any insight into why the winter 1933-34 was such an extremely warm winter in the Western US, in spite of a La Nina? The temperature anomalies that winter make absolutely no sense. I have been trying to figure out what went wrong with that winter for years. There is no question it's starting to bug me a little bit with this endless ridging in the West.

Thank you!


Ed Berry said...

Hi Jim,

As you know, I cannot answer that question without data (which may be relatively limited for 1933-34). Responses in the atmosphere are all too often non-linear, etc.

From what you describe, there was ridging across the western USA. During this fall (2008) ridging has been occurring along the west coast in a La-Nina base state. We can link episodes of RWDs from the twin subtropical west Pacific Ocean cyclones arcing to the ridge. Of course, there are seasonal cycle issues, and this is not suggesting this was the case during 1933-34.


Captain Climate said...

Predicted recurve of a West Pacific Storm an indication of a stay of a "La Nina" execution of cold in the east? It is a learning experience to look at numerical models then make corrections to the biases using the GWO/MJO composites.

Following the ups and down of AAM is opening my eyes to how some of the old weather adages work/

Thanks for your hard work and sharing it with the public.