Saturday, December 27, 2008

Shifting Around in the Atmosphere’s Witches Brew

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.

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 tentatively planned for 24 February 2009 on the WB (2009) GWO. Details are still being worked out, and stay tuned for our announcement.

This is little overall substantial change to the spatial distribution of global SSTs. The warmest ocean waters extend from the extreme west central Pacific to ~10S/160E with totals ~30C and anomalies roughly 1C. There has been some recent cooling of Eastern Hemisphere tropical SSTs due to persistent enhanced rainfall (more said below).

Significant negative anomalies have evolved along the equatorial Pacific Ocean cold tongue, responding to (as was expected) the global ocean-land-atmosphere dynamical system being tilted toward La-Nina. Numerous past discussions have addressed a few of these important scientific matters. Magnitudes along the cold tongue are generally minus 1-1.5C, with totals well under 26C east of the 0/160W. At least from the subseasonal perspective, our La-Nina encore is anything but “weak, transient, still neutral, cannot happen because of the seasonal cycle (good eating for the Rottweiler!!!) , etc…………” (note the initial projection) (link 18).

The rest of this discussion is abbreviated due to “holiday constraints”. That said there is not much new additional information to offer to that already written since at least the 22 November 2008 posting.

The wind and tropical convective signals are getting better aligned as the quasi-stationary La-Nina base state matures. Tropical convective forcing has loosely consolidated ~5N/125E while extending from the equatorial Indian Ocean into the warm southwest Pacific. There has been some shifting around of components, including the recent excitation along the SPCZ. However, any real MJO signal is weak. I think the roughly 2 sigma projection (26 December) in octant 4 of WH (2004) phase space retaining the ENSO and interannual components is a response (really a computation) to the wind and convective signals syncing up. Phase 4 of the 250mb snr composite anomalies of psi (olr) reasonably depicts tropical circulation anomalies (convection).

Global relative AAM (through 25 December) has dipped to ~1 sigma below the R1 data climatology, the lowest since at least October. I do think this global signal will continue to decrease at least into next week. The various terms of the global and zonal mean AAM budget generally reflect our La-Nina. For instance, the global frictional torque and earth AAM are slightly positive, with zonal mean contributions coming from enhanced Northern Hemisphere trades and high surface pressures across the midlatitudes. The latter are a response of the current strong positive phase of a Branstator (2002) circumglobal teleconnection of anomalous ridges. Contributing to a well-defined interhemispheric meridional symmetry of zonal mean zonal wind anomalies, easterly wind flow is very intense across the subtropical atmospheres. In fact, zonal mean easterly wind flow anomalies ~30N (shifting south for the past several weeks) are roughly 10m/s.

The WB (2009) measure of the GWO may be “settling down” in octants 1-3 of phase space. However, whether or not that becomes a JFM seasonal mean is unclear. The roles of possible additional MJO variability and/or the southwest Pacific Ocean have already been discussed. However, I think some rendition of a superposition of tropical and extratropical circulation (rainfall) anomalies depicted by the 250mb snr composite psi (olr) anomaly plots for phases 3-4 of both the MJO and GWO are a possibility. That suggests a continued loose preference for an East Asian trough-central Pacific Ocean ridge-west and central North American trough.

There will be transient synoptic variations including those linked to fast GWO orbits. Case in point, the west coast ridge/eastern states trough predicted by many week-2 numerical model ensemble means is not unrealistic (a feedback in this case). What may be least likely is a JFM seasonal mean outcome of an extended and southward displaced North Pacific Ocean jet leading to a downstream split flow pattern and a tilt toward (such as) cold/wet across the Deep South of the USA (typical of GWO phase 7, El-Nino base state).

USA and international weather ramifications should be well understood by now. For example, continued excessive rainfall from most of Indonesia into portions of Australia “UFN”. Please see all the snr composites per ESRL/PSD GSDM web link for details. We are actually going into week-5 per the 22 November 2008 posting. It is interesting that what many define as a reverse or negative phase of the Pacific North American teleconnection pattern (-PNA/RNA) appears to be relaxing, at least for the time being. Stay tuned.

I trust the expertise of the appropriate meteorological centers to alert the public of additional weather hazards worldwide, including official statements for tropical cyclones that may impact regions such as around Australia during the next several weeks. Episodes of global extreme weather events continue; for instance, the recent heat and flooding across portions of Brasil.


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 at least an abbreviated discussion the weekend of 3-4 January 2009.

Ed Berry


jam472 said...


Enjoy you blog. In your opinion, how long do you think we will see the positve PNA on the West Coast last for. The GFS and the EC have the +PNA for at least 3 weeks, as I don't see it breaking down on the ensemble members.

Your insight would be appreciated.


NWS Spotter LAC 254

Captain Climate said...

Hello Ed;

I found it interesting in the Low-AAM decade of the 60's that the Southeast averaged cooler in terms of surface temperature while the west was warmer.

Is there a tipping point when feedback to oceanic cooling on land leads to inverse outcomes (cool/wet where previously warm/dry)?



Ed Berry said...

Hello Jason and Dean,

Thank you for the questions. About the +PNA possibility, should that occur during ~later week 2 into 3, I do think it will be transient. In some sense, this behavior is similar to the perturbations we had on La-Nina a year ago.

We are seeing a GWO feedback leading to an eastward shift of convection into roughly the SPCZ and a subsequent extended North Pacific Ocean jet. There is already evidence westerly wind flow is accelerating in the NH zonal mean subtropics (~30N). However, "things may snap back" afterward. That typed, the southwest Pacific Ocean is anomalously warm, and if a fundamental circulation change is to occur, now is the time given seasonal cycle issues. We will carefully monitor.

This situation may lead to high impact weather affecting a large part of the country roughly mid-late next week. That includes more Arctic air perhaps focussed on the Northern/Central Plains and heavy precipitation possibly most intense across the Plains and Ohio Valley. Any yes, there may be an East Coast storm situation before this is "all said and done".

Dean, that would be something I would have to look at carefully. There are a lot of issues, including starting with the data sources. Regardless, every year is different and there are no "magic numbers". Non-linear feedbacks (like we are observing right now) always happen, and can/do lead to less probable seasonal mean outcomes. The latter further emphasizes the need for linking weather and climate (understanding subseasonal variability) and daily monitoring.


snoman said...


I am no Ed Berry but I do have a few thoughts about your question. There are a few possible reasons the SE was so cold in the 1960s and the NW was warmer. In the late 1940s and 1950s the NW had an extreme cold period that was apparently caused by a combination of very low PNA, low AAM, very low PDO, and high AMO (Atlantic Multidecadal Oscillation). In the 1960s the AMO very suddenly flipped to negative at the same time the PDO and PNA moderated a bit. The reuslt was a switch to a much colder east and warmer West (although the West still had some very cold winters thrown in during the 1960s). At present we seem to be in more of a 1950s regime with very low PDO and fairly high AMO.

I hope this helps.


Ed Berry said...

Jim and others,

Thank you for the comments and interaction! I just published another discussion.

I think it would be very interesting to examine the GWO with other diagnostics for interdecadal and related variations. That would help us with subseasonal and seasonal forecasts. Right now, I have to "take one thing at a time". For example, what would the composites look like with the ENSO signal left in, especially for the MJO?

All the best,