Friday, November 14, 2008

Wrong Turn in the REAL Atmosphere???

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 now updated daily, centered on the date shown. Please see product descriptions. WB (2008), 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.

The warmest SSTs globally persist ~140E within 20 degrees of the equator having totals ~29-30C but with weak anomalies. Larger positive anomalies ~1-2C are in the region of the equatorial Indian Ocean with totals near 29C. A strong equatorial trade wind surge (~10m/s anomalies) continues from ~140E to east of the Dateline. There is upwelling of the oceanic thermocline east of the Dateline, leading to roughly negative 2-3C subsurface anomalies ~100-200m depth along the equator per latest 5-day averaged TAO buoy data. Remember that these anomalies are in the presence of annual cycle cooling. SST anomalies ~minus 1-2C are also present from about 160E-140W within 10 degrees of the equator.

Bottom line, I think we may be waiting for the tropical Pacific Ocean “SSTs to really kick in” responding to the global circulation already having La-Nina characteristics. In fact, speculating, are we starting an evolution of another SST cold event which may mature as late as 2009-10 that will even make the Nino 3.4 people happy? See links below. (note the initial projection) (link 18).

I would like to keep this discussion relatively brief. The subseasonal behaviors of several components involving the earth-atmosphere-land dynamical system have not played out as I expected during the last few weeks. However, what has occurred does not surprise me. Regardless, this is an example of why rigorous daily monitoring within the WB (2007) GSDM framework is critical, and relying on the numerical models (multi model ensembles) alone is scientifically unrealistic and indefensible. Furthermore, empirical techniques employed by some synopticians to track baroclinic signals on Hovmoller diagrams as a predictive tool many weeks in advance also has little scientific merit.

Eastern Hemisphere tropical convective forcing has been shifting west during the last week or so, and is currently focused around 5N/100E. Intense to severe tropical thunderstorm activity extends from near 60E to western Indonesia and covers most of the Bay of Bengal, including a tropical cyclone about to impact India. The latter is approximately 35 days after the last period of enhanced rainfall in that region, and it is possible a MJO component may evolve. Leaving the interannual signal in, there is about a 2 sigma projection in octants 3-4 of WH (2004) phase space. A faster signal tied to the WB (2008) measure of the GWO has led to some convective enhancement across the Western Hemisphere. The recent flooding rainfall across the USA Pacific Northwest is attributable to an “atmospheric river” of moisture transport from the Eastern Hemisphere tropical convection.

Phase 4 of the WH (2004) MJO snr 250mb composite psi anomaly plots reasonably depicts the current tropical circulation. In fact, per animations of upper tropospheric daily mean vector wind anomalies, the spatial pattern of Indian Ocean anticyclones and west Pacific cyclones is similar to a couple of weeks ago. The notion offered that the opposite sense to this phase would not be as robust was correct.

So, what happened? Obviously not the coherent eastward shift of tropical forcing/circulation behavior from the Eastern into the Western Hemispheres I discussed was likely in my last several postings. Nevertheless, I do feel there is a scientifically defensible attribution, and this will be one of the many foci of WB during the next several weeks. I think dynamical processes explained by the WB (2008) measure of the GWO contributed, starting with the ~3 sigma orbit in octant 4 of phase space during mid October. Poleward AAM transports and surface torques created a large tendency working to increase zonal mean westerly wind flow in the subtropical atmospheres.

Cutting to the chase, it is possible Rossby wave energy dispersions (RWDs) linking the tropics and extratropics (fast GWO) worked to oppose this tendency, wanting to retain the global circulation in “La-Nina”. Specifically, and beyond the scope of this discussion, the latter is in reference to complex dynamics working to reduce global westerly wind flow, best represented synoptically by ~phase 3 of the WB (2008) GWO 250mb snr composite psi anomaly plots. That is, a positive phase of the Branstator (2002) circumglobal teleconnection of anomalous midlatitude ridges, observed during the boreal winter of 2007-08. Please remember that I am talking about forcing-response-feedback relationships and the not the unrealistic notions of equilibrium states (ex., Charney and DeVore 1979).

Currently, and loosely similar to about a month ago, there is an interhemispheric signal of poleward AAM flux, ~45N and 50S. The global surface torques is positive including a ~20 Hadley East Asian mountain torque (see AAM plots for details). A synoptic response has been for a cold outbreak off the coast of China and an expanded North Pacific Ocean jet. This is an example of a situation when the jet “outruns” the Eastern Hemisphere tropical convective forcing. Phases 4-5 of the WB (2008) GWO snr 250mb composite psi anomaly plots best depict the extratropics, and should through at least week-1.

What road the atmosphere takes from here is extremely uncertain, particularly for timing and details. Statements such as forecaster confidence of something like 4 on a scale 1-5 for a USA week-2 prediction of temperature and precipitation anomalies are unrealistic. The numerical models have been inconsistent, to say the least, for the last 1-2 weeks. The tropics and extratropics are still out of sync.

That said, what appears most probable is for a GWO 8-1 transition ~weeks 2-3 per above, then perhaps coupling of the tropics and extratropics across the Eastern Hemisphere weeks 3-4.That is, possibly a superposition of the circulation states shown by the GWO/MJO phases 3-5 of the snr 250mb composite psi anomaly plots during the first half of December. Given base state issues briefly discussed above, I do feel confident that the La-Nina side of phase space is the most probable “until further notice”.

Weather ramifications include above (below) average temperatures returning to the eastern (western) USA during roughly week-2/3 along with an active southwest flow storm track on the Plains. Much of the west coast could receive generous precipitation. Anomalous cold may then focus on the central states afterward. Interestingly, what may actually occur is ~1-2 week delay of the outlook statements offered in past postings. Monitoring is critical, including the future of the Eastern Hemisphere tropical forcing, which will impact the USA. The risk of extreme weather events (ex., blizzard conditions and severe thunderstorms) affecting large portions of the country, including having adverse impacts on Thanksgiving and even Christmas travel, is possible to be elevated the next several weeks.

It is unclear if and when the above mentioned tropical forcing will coherently shift east. However, locations from the west central into the Southwest Pacific Ocean are probable to be at risk from severe rainfall and cyclones ~weeks 2-4 (week-1 understood). Generally climatological precipitation should continue for tropical South America and Africa the next several weeks. It is not out of the realm of possibilities to see multiple regions of enhanced tropical convection during the next several weeks, but with a focus shifted toward the Indian Ocean and Indonesia ~100-120E (as part of what may be an emerging quasi-stationary component of a La-Nina base state).

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.


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:

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 22-23 November.

Ed Berry


snoman said...

Hi Ed,

Fabulous discussion as always!

If you had to come up with a probability of an Arctic outbreak hitting the Pacfic Northwest this winter what would it be? It would seem that some degree of a La Nina and very low PDO should at least give us a shot at it.

Thank you!


Ed Berry said...

Hi snoman,

Thank you for the comment. Of course, I cannot come up with a quantitative probability. If a stronger La-Nina situation is evolving, I agree the odds shift above climatology for an Arctic outbreak to impact the Pacific Northwest this winter. In any case, we will need to monitor for this.

Thank you,

snoman said...

I figured you wouldn't go out on that kind of a limb! On the subject of La Nina; is an "atmospheric" La Nina likely to have the same effects as a La Nina where the SST's are on board also? The latest MEI values are actually lower than some past La Nina events. This is certainly one strange year!


Ed Berry said...

Hi Jim,

That is a good question about an
"Atmospheric La-Nina" vs. a coupled situation. A synoptic response is as shown by the snr 250mb composite psi anomaly plots for GWO phase 3. I would have to look at lots of cases to fully answer. In any event, the sample size from the real atmosphere is not large.


roqs2stoned said...

Ed, That was a great discussion but I am concerned that it is incomplete. Currently, the development of La Nina is being blocked by an oceanic Kelvin wave that is moving east along the equatorial pacific. I did not see much in your discussion about how sst's affect the atmosphere above when in fact it is extremely important, especially in the Nino regions.


snoman said...

I just had to comment on Mike's post. If there is an oceanic Kelvin wave how is that possible? We have had multiple strong trade wind bursts over the past several weeks. The SOI is at levels one would expect during a moderate to strong La Nina. On the other hand I am puzzled how it is possible the ENSO SST's are not cooling with the atmosphere in the state it's in.

roqs2stoned said...

Snowman, Ocean water in the equatorial pacific has it's own behavior as part of the ENSO cycle.
NOAA has a pretty good presentation on the oceanic kelvin waves here:

Flip down to the "Expert Discussions / Assessments" section and look at either the pdf or powerpoint presentation on "Weekly ENSO Evolution, status, and prediction presentation" It is the 16th frame in the powerpoint presentation.
The Kelvin wave is the reason it's not cooling right now.

Ed Berry said...

Mike and snoman,

Thank you for the comments. This is good discussion.

First, it is simply "impossible" for me to discuss "everything", especially with the SSTs. That is why I provide the links. However, we are very diligent with all matters including the above. Hopefully this effort will become more formal sometime "soon".

Secondly, in regard to the SSTs impacting the atmosphere, kindly stated, "tell me about it". When I discuss the role of SSTs I am refering to the global tropics and related interactions. Simply focusing on the Nino regions is incomplete. For example, I can probably present a defensible argument that the anomalously warm Indian Ocean helped to shut down the 2006-07 El-Nino. Furthermore, the latter was involved with the initiation of the subsequent cold event. Point being, it is important to understand the dynamics of subseasonal variability including ocean-land-atmosphere interactions.

Finally, I think some care needs to be taken about the oceanic Kelvin wave "keeping the (subsurface) SSTs warm". I submit you may be observing a response to a respite in the trade surges that snoman mentioned. The trades remain enhanced and the SSTs are cooling. How strong this resurgence of La-Nina will be is unclear (yes, PDO notions well understood). In any case, this situation is extremely complicated and we need to avoid "blanket statements".


roqs2stoned said...

Hi Ed,
I was mainly referring to the Nino regions because the subject seemed to mainly focus on whether or not La Nina would re-emerge.
My understanding is that the atmosphere follows surface conditions. For instance, the 2006 / 7 El Nino followed it's course and a response by the oceans is what ended it, ie: when the warm pool moved to Peru it blocked upwelling (flattened out the thermocline), then as it struck the Peru coast it bounced back and pressuer from the blocked upwelling quickly pushed cold water to the surface. When the surface cooled near Peru, the atmosphere off the coast responded, essentially sinking. When the air sank and it reached the surface then began moving west, pushing more surface water west, causing more upwelling and thus the 2007 / 8 La Nina. As for PDO, it appeared that prevailing winds (and probably ekman transport) brought cool anoms from the Baja coast into the Nino 3.4 region which stopped the westward propagation of the warm tongue that developed off Peru in mid 2008. During all of these events, there were complications by oceanic Kelvin waves. Anyway, that is whaere my observations lead me... too bad they do not have complete bouy arrays all over the entire globe, this would be much easier.