Friday, October 24, 2008

Update – Bear Atmosphere Stimulus???

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.

This discussion will be limited given time constraints. The 91-day signal to noise ratio (snr) anomaly composites are now updated daily, centered on the date shown. Please see product descriptions. Part-1 of WB (2008), where the GWO is formally introduced, is in press for publication in MWR. Please see link in Appendix.

SSTs have cooled across the equatorial Indian Ocean as a response to intense rainfall. Significant cooling has also been occurring in the region of the equatorial Dateline to Indonesia, as a result of a strong trade wind surge. For instance, the 29C isotherm has shifted back to ~160E. The latter may be the initiation of a coupled ocean-atmosphere response toward La-Nina, which has been the character of the global circulation for the past several weeks and longer. Stay tuned, and see links below. (note the initial projection) (link 18).

A large amplitude subseasonal event, the strongest since at least last May, involving multiple time scales is in progress. Since the start of this month, the WB (2008) measure of the GWO has done a good 2 sigma orbit in phase space, reaching octant 4 about a week ago. As I type the GWO (updated through 22 October) is collapsing toward octants 8-1. The WH (2004) measure of the MJO (through 23 October) has ~2 sigma projection in octant 4 of phase space. However, that projection increases to roughly 2.5 standard deviations in octant 3 retaining the ENSO signal (more realistic).

Per full disk satellite imagery and animations of upper tropospheric daily mean vector wind anomalies, phases 3-4 of both the GWO and MJO snr composite 250mb psi anomalies nicely depict the global circulation. There is strong meridional symmetry of zonal mean zonal wind anomalies, including anomalous midlatitude ridges.

The eastward shift of tropical convection from the Indian Ocean into Indonesia, working dynamically with coupled processes involving the surface torques, poleward AAM transports and extratropical eddies have attempted to shift the atmosphere away from the La-Nina attractor. In fact, global relative AAM recently spiked to a slightly positive anomaly. However, there has been a greater removal of anomalous zonal mean easterly wind flow from the subtropical atmospheres than actually adding westerlies. Having my reasons, analogous to recent failed financial stimuli to save the on-going collapsing global stock markets, the same may be true for the atmosphere.

There is no change to my speculative outlooks from past discussions. My confidence would be higher if I was doing this writing a month from now given seasonal cycle issues. For example, meridionally directed Rossby wave energy dispersions (RWDs) forced by west Pacific Ocean tropical convection is more likely to impact North America during boreal winter than autumn.

Observational evidence suggests a quasi-stationary component of the tropical forcing (~90-130E per OLR time sections)/global circulation anomalies may be emerging. However, going along with the GWO (keeping in mind rapid variations), I do think it is probable there will a signal of tropical forcing propagating first into the west central Pacific, then Western Hemisphere by roughly week-3, perhaps sooner (noise understood). Hence an evolution of anomalies shown by phases 3-5 of both the MJO and GWO composites of snr 250mb psi anomalies is probable weeks 1-2. A “jump” to phases 7-8-1 circulation anomalies shown by particularly the GWO composites may be reasonable weeks 3-4. The latter suggests anomalously strong troughs to impact the western USA leading to an active southwest flow storm track on the Plains. A cold regime, characteristic of ~GWO phase 3 focusing on the middle of the country, may evolve during December.

Internationally, intense to severe thunderstorm clusters will continue to impact the Bay of Bengal into Indonesia week-1, shifting slightly east week-2. Locations from Southeast Asia through the Philippines as well as portions of the southwest Pacific Ocean may experience intense rainfall weeks 2-3. The tropical cyclone hazard is unclear; however, I think it is unlikely to observe a westerly wind event of the same magnitude as the current trade surge west of the Dateline. The tropical Americas including portions of Brasil may experience a significant increase in rainfall perhaps by late week-2.

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 last week, including locations such as Honduras and Morocco.


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 (2008)), has been accepted for publication MWR. A pdf of the in press version can be downloaded from the following link:

We hope additional overlapping seasonally varying global and zonal mean subseasonal composites for variables such as surface air temperature, precipitation, geopotential height, winds and streamfunction anomalies can be posted on the ESRL/PSD GSDM web site. Part-2 of our 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 complete discussion the weekend of 31 October-2 November.

Ed Berry


snoman said...

Hi Ed,

You talk about the cold December being focused in the center of the country. Do you see anthing good for the Pacific Northwest. We have been waiting forever for a cold winter here. I notice the CPC shows us cold Jan - Mar which almost left me speechless!

steve said...

Great work, as usual!!

I have 2 questions:
given the "tilt toward a La-Nina seasonal base state", which kind of winter Weather Regime (Robertson and Ghil) do you think will be the dominant one over the North Pacific / North America sector next winter?
And what is your opinion on Euro-atlantic sector?

Thanks for your very interesting posts.


Ed Berry said...

Hello Snowman and Steve,

Thank you for the positive feedback. For lots of reasons uncertainty for the outcome of DJFM may be higher than "usual". The CPC temperature forecasts are largely from their consolidation tool while I am using information derived from subseasonal dynamics to offer hopefully useful speculation (at this point).

A La-Nina global (not based on Nino 3.4, etc.) circulation base state favors anomalous midlatitude ridges including the central/east Pacific Ocean. That suggests western USA troughs shifting into the Plains along a SW flow storm track. However, this can be variable. The 2007-08 boreal winter was exceptional for persistence particularly JFM. At times, much of western and northern Europe can be hammered with troughs coming off the Atlantic Ocean during a La-Nina base state.

Ed Berry