Saturday, May 02, 2009

Atmospheric MAYhem???

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. Partially linked to the seasonal cycle, the warmest SSTs globally are across the equatorial Indian Ocean, with totals in excess of 30C and anomalies ~plus 1-2C. Exceptionally strong convective suppression during at least the past couple of weeks has also contributed to these warm waters. SST anomalies across all Nino regions are loosely slightly positive. Recent surface westerly wind anomalies have assisted with this warming. However, the 29C isotherm is still west of the Dateline on the equator. Regardless of whatever viewpoint anyone chooses, scientifically, the future course of ENSO (global ocean-land-atmosphere dynamical system perspective) is unclear. Historically, weather-climate events (surprises?) during May can provide some insight.

/enso_update_latest.html (note the initial projection) (link 19)

Per WH (2004) measure and other tools, the moist convective signal with the ongoing strong MJO is propagating through the Western Hemisphere as I type. Updated through 1 May there is still well over a 2 sigma projection in octant 7 of WH (2004) phase space. Broadly, during the last couple of weeks numerical models have tended to weaken this signal too quickly and have been too slow with the eastward propagation. A large contribution to the MJO projection has been the Indian Ocean suppression mentioned above.

Moist tropical convective forcing has already propagated poleward off the equator across the west central Pacific, increasing the tropical cyclone hazard in the region of the Philippines. The accompanying surface westerly wind flow anomalies are also shifting away from the equator into the both hemispheres along and west of the Dateline. Meanwhile, moist convection is increasing from Central and South America into equatorial Africa. There is some “sputtering” along the east Pacific Ocean ITCZ, and working with the extratropics, a relatively moist subtropical jet (STJ) is directed toward the southern USA states assisting with rainfall production. The latter is consistent with phase 7 of the MJO, which is an EL-Nino like circulation response per WB (2009) GWO phase space. However, cutting to the chase, there are still non-trivial La-Nina characteristics to the global circulation, and the above mentioned STJ is rather “pathetic”.

There continues to be the lack of a significant projection in phase space of the WB (2009) measure of the GWO (since ~1 April). Recall (again) that the GWO is a global dynamical measure of the atmosphere, whereas the WH (2004) empirical MJO measure only considers lower and upper tropospheric winds with OLR anomalies within 15 degrees of the equator. From the global perspective, there has been a weakening La-Nina allowing relative AAM to return to about normal per R1 data climatology. In fact, through 30 April relative tropospheric AAM is slightly above normal. Additionally, AAM tendencies have not been large (for reasons), all combining to give the appearance of a weak GWO signal.

However, zonal mean and regional scale GWO components, as well as individual terms of the earth-atmosphere AAM budget have been anything but weak. These include Eastern Hemisphere subtropical wave trains that excited the 2 (stochastically forced "cheap") MJOs in the region of Indonesia during the past 4-5 months, and roughly 20-30 day variations of the global mountain torque. Through 30 April the global frictional torque has dipped to below minus 10 Hadleys largely from frictional dissipation of recently added westerly wind flow. That is the lowest since about mid-January. The frictional dissipation has not only occurred in portions of the tropics/subtropics (tied to the MJO), but also across the extratropical storm track regions. My suspicion is there may be a large negative AAM tendency during the next couple of weeks (more said below). Is it time to “short the atmosphere”?

Regardless of details, a superposition of phase 7 for both the GWO and MJO snr 250mb psi composite anomaly plots best depicts the current global circulation. For example, there has been subtropical transition of Eastern Hemisphere upper tropospheric circulation anomalies, and a “poor excuse” of an extended north Pacific Ocean jet has occurred. These behaviors were expected per past discussions.

It is relatively clear to me that a GWO/MJO 7-8-1-2 transition is in progress (a.k.a. a low to high zonal eddy wave number transition response across the Northern Hemisphere extratropics). The corresponding snr 250mb psi composite anomaly plots should depict the expected synoptic behavior of the atmospheric circulation over the next few weeks. The probable response for other variables such as anomalous 2m air temperature across North America can also be determined from the composites (we hope to add more variables). This evolution should go through its life cycle by roughly later week-2/week-3. Numerical models already have been, and will continue to struggle (in addition to seasonal transition issues).

Enhanced moist tropical convective forcing is likely to return to the Eastern Hemisphere including the Indian Ocean/Indonesian regions during weeks 2-3. However, uncertainty issues include persistence, and whether or not the MJO signal will continue. In any case, it is during this period that AAM tendency may become strongly negative contributing to a strengthening projection of the GWO perhaps in octants 2-3 (back toward La-Nina) of phase space by week-3. Disciplined serious daily weather-climate (WB (2007) GSDM sense) monitoring is critical UFN to gain a better understanding of the course of any additional subseasonal activity and possible ENSO ramifications. Using models as a stand alone is anything but scientifically complete and defensible. Synoptically for the USA, other than being about a week later, there is little change from what I typed in my 24 April posting.


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 are working to mainstream this effort. The support is very much appreciated!

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 complete 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 Rex the Rottweiler VERY angry! I am planning on posting a discussion next weekend, 8-10 May.

Ed Berry


sirvatka said...

Someday I want to do the correct reading and understand all this. I hope I can ask a question of two a week and perhaps I will understand some before that. Here is my question: With low AAM, we are looking at highly meridional flow? High AAM is stronger than normal zonal flow?

weatherBTL said...

Well, it seems that the MJO triggered a welcomed round of wet weather from northern California northward over the last week+. With the MJO propogating eastward and then back into the Indian Ocean, do you still believe that progressive troughs will push across the west and central US sometime between late May and early June? Appears CPC is on board with this idea. I'm going from memory from your past blogs about expectations, so I hope I haven't misinterpreted! Thanks for your expertise! Brett

Captain Climate said...

It has been interesting to see the MJO slow to a crawl then reverse. I wonder if the uptrend to higher pressure over Northern AU is a sign of at least a short term 'regime change' from low AAM dominated weather? Speculation seems rife about a Winter El Nino. I am skeptical .....

Ed Berry said...

Hello sirvatka,

Sorry for my slow response. Please feel free to ask questions anytime. I do my best to get back.

Broadly, high (low) AAM is stronger (weaker) than normal global westerly wind flow, favoring a southward (northward) shifted storm track. Intense (weaker) zonal flows tend to dominate the (continents) oceans during high (low) AAM. Low (high) pressures tend to dominate the subtropics and even midlatitudes during high (low) AAM regimes. High (low) AAM is often characteristic of El-Nino (La-Nina).

During the last couple of years the atmosphere has generally been low AAM due to La-Nina. That is one reason for periods of excessive dryness across the southern USA.

Hope this helps,

Ed Berry said...

Hello Brett and Captain Climate,

I am planning on doing a post tomorrow (5/9), so hopefully that will answer some of your questions. At this point I almost feel like "punting" given the mess our weather-climate situation has become along with my poor assessments.

Regardless, consolidation of tropical forcing should occur across the Eastern Hemisphere during the next few weeks and I would expect a large negative AAM tendency "soon". Perhaps by week-3 we will see a response depicted by snr phases 2-3 for the GWO with MJO phases 4-5 (OLR, PSI, etc).

Take care,