Saturday, April 11, 2009

Strong MJO and Transitioning Toward ENSO Neutral: End of Story – Correct???

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. Very warm SSTs continue across the Indian Ocean into the southwest Pacific, with totals ~29-30C and anomalies roughly plus 1C. However, the recent increase of intense to severe tropical convection in the area of 60-110E slightly north of the equator has started to cool the ocean waters in that region.

Flanked by weak warm anomalies ~plus 0.5C, similarly cool SSTs are present around 140-170W across the equatorial Pacific. Totals have warmed to ~26-28C over much of Nino 3 region; however, the 29C isotherm is still well to the west ~165E on the equator. Substantial warmth is still present at depth along the equatorial thermocline west of 160W at ~100-200m per latest 5-day averaged TAO buoy data. Magnitudes are around plus 2-4C.

Worth repeating from a week ago, only a few scientific matters can be discussed in this forum. Several very serious weather-climate monitoring issues exist that careful attention must be paid to heading into boreal summer. These include warming of the west Pacific Ocean should westerly wind bursts start to occur on the equator, while atmospheric dynamical processes stubbornly try to maintain La-Nina. It is also important to keep in mind “the fundamentals,” and not get caught up in overly simplified “cookbook measures” such as univariate ENSO indices (ex., the ONI) as well as those involving the MJO. In the following, I am again challenged to write about complicated and somewhat conflicting signals. (note the initial projection) (link 19)

The most robust subseasonal signal continues to be the (pseudo) MJO. Per WH (2004) technique, through 10 April ~2.5 sigma projection in octant 2 of phase space was observed, approaching 3 standard deviations emerging into octant 3 retaining the ENSO signal (more realistic; constructively interfering with La-Nina). Full disk satellite imagery shows intense tropical forcing centered ~5N/90E, and subtropical transition to upper tropospheric twin Indian Ocean (west Pacific Ocean) anomalous anticyclones (cyclones) is occurring as I type. Furthermore, zonal mean upper tropospheric anomalous easterly wind flow is returning to the deep tropics (~5m/s at 250mb). More said below.

Sparing other details about what appears to be a real “text book” MJO, the reader may ask, “why am I complaining about it?” As was discussed in my 4 April posting, driven by stochastic dynamical processes explained by the WB (2009) measure of the GWO, this MJO grew out of the noise in the region of Indonesia. Furthermore, to state that there are similarities involving this event with the rogue MJO during late December 2008-January 2009 is anything but scientifically defensible in terms of complete understanding.

My point is that I am confident the area of enhanced tropical rainfall centered west of Indonesia is unlikely to coherently propagate eastward into the central Pacific Ocean on the MJO time scale. I do think the latter will contribute to reinvigorating our on-going quasi-stationary La-Nina base state (subseasonal time scale), and if there is an eastward shift, that may occur abruptly per GWO OLRA composites. Finally, I also feel that just as this MJO signal grew out of the noise in the region of Indonesia during mid-late March, it is also probable to decay in that region during the next few weeks. Yes, the Rottweiler has been licking his chops during this “MJO situation” the last few weeks!

As suggested above, our La-Nina base state is “reloading”, at least in terms of the zonal mean and the return of the expected asymmetric zonal wave number 1 pattern of tropical circulation anomalies. For instance, persistent anomalous easterly wind flows through out the global subtropical atmospheres (near 15-20S and 25-30N) is beginning to shift equatorward linking up with the deep tropical anomalous easterlies. Phase 3 of the MJO ~250mb snr psi composite anomaly plot reasonably depicts current tropical circulation anomalies. Global relative AAM, updated through 8 April, has been hovering ~1 sigma below the R1 data climatology. Holding it up, so to type, has been yet another one of those complicated feedbacks having details impossible to write about here.

Global relative AAM tendency has spiked to ~plus 20 Hadleys, forcing the WB (2009) measure of the GWO toward octant 4 of phase space while shifted toward the La-Nina attractor. Carefully studying various animations suggests that it is reasonable to submit that what was first a strong positive East Asian ~20 March then global mountain torque ~1 April had a contribution from the past southwest Pacific tropical forcing. Working with other extratropical processes, the linkage was established via Rossby wave energy dispersions (RWDs) from the south Pacific forcing. These were phased properly to favor anomalously high mean sea level pressures on the eastern sides of major mountain massifs including East Asia and the Andes.

A synoptic response for the USA was initially an active southward shifted storm track late March and then more recently split flow expanding into the western states from the Pacific Ocean. The latter has helped to maintain the active southern branch of the westerlies, bringing much needed precipitation to areas experiencing severe drought. Sparing details (again), the more sophisticated readers will see there is even a weak signature of the split flow from the AAM transports plot. I do think this situation is about to end.

Broadly, where do we go from here? My feeling is that the tropics and extratropics will start to sync up better during the next few weeks, meaning that global AAM tendency is likely to become negative “soon” as both surface torques may contribute. I also feel there will be lingering La-Nina circulation anomalies, particularly in the zonal mean, well into boreal summer. Anomalously strong zonal mean easterly wind flows across the Southern Hemisphere subtropical atmosphere this upcoming austral winter may provide a clue of what to expect for the Northern Hemisphere 2009-10 cold season.

Repeating one of my standard excuses, any subseasonal outlook this time of year has higher uncertainty, and our current situation is adding to it. That typed, my offering that the ~250mb psi snr composite anomaly plots for GWO phases 4-5 for week-1 last weekend worked out okay. Per above, there has been extension of the jet across the north Pacific Ocean but poleward shifted in our La-Nina situation, leading to the current USA split flow. During week-1 phase 1 of the GWO snr ~250mb psi (and other variables) composite anomaly plot is likely to depict the global circulation. With somewhat high confidence, I think a superposition of anomalies shown by phases 4-5 of MJO ~250mb psi snr composite anomaly plots (representing the quasi-stationary La-Nina) with phases 2-3 of the GWO are probable during weeks 2-4 (timing may be golden; however, it is in the noise after week-1!).

Synoptically for the USA, and most numerical models are doing a reasonable job into days 5-7, another western states split flow closed low is likely next week. Afterward (roughly week-2), this split flow should consolidate while the “northern branch ridge” retrogrades. Hence there is likely to be a period of an east Pacific Ocean trough-western states ridge and so forth. Perhaps similar to many episodes during spring 2008, ~weeks 3-4 a resumption to strong but progressive western and central USA troughs may resume. Should we go back to that northward shifted but active storm track, drought may return/intensify across the southern USA once again. Speculating farther into summer, should this La-Nina situation linger and excursions into octants 4-5 of GWO phase space occur, like summer 2008, there may be episodes of anomalous heat contributing to elevated fire dangers across the western states.

Other weather ramifications, nationally and internationally, should be understood. For instance, more western USA “trough attacks” are likely to make the storm chasers happy across the Plains, and the concern for Bay of Bengal (and possibly Arabian Sea) tropical cyclogenesis may increase substantially during the next few weeks. On the latter, there are already 10-15m/s surface westerly wind flow anomalies along and north of the equator across the Indian Ocean.


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 appreciate all the support!

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 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 the Rottweiler VERY angry! I am planning on posting a discussion next weekend, 17-19 April.

Ed Berry

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