Saturday, May 03, 2008

Exorcism Falling Short???

SSTs from the tropical Indian into the Pacific Ocean basins loosely exhibit a spatial cool-warm-cool anomaly pattern. Anomaly magnitudes are approximately 1-2C for the cool and roughly 0.5-1C for the above average waters, latter centered in the region of Indonesia. SST totals are generally in the 28-30C range west of the date line. An interesting observation is that this spatial pattern of Indo-Pacific SSTAs is essentially opposite to that during boreal fall-winter 2006-07.

The La-Nina component of these SSTs has weakened considerably during the past 1-2 months. Latest 5-day averaged TAO buoy data shows that these cool anomalies extend only to a depth of ~100m, while positive anomalies ~4-5C persist at approximately 200m deep west of the date line. The warm horseshoe spatial SSTA pattern is still well defined from Indonesia into the extratropics of the North and South Pacific Ocean basins, while local El-Nino SST conditions are present west of South America. The reader can refer to the links below for additional SST details.

The point I want to make is there still exists no observational evidence of a coherent evolution toward an equatorial Pacific Ocean warm event. A few of these matters will be discussed below. In general, there are an endless number of scenarios anyone can propose for global SSTs numerically, statistically, both, etc. These can include the IOD, ENSO, PDO, AMO, and so forth. Whatever the case, confidence in any predictive scheme is currently low no matter what is offered. Careful detailed rigorous daily monitoring within a dynamical framework of weather-climate linkage is a must to gain some understanding on the future of El-Viejo, etc. The current global circulation base state is still La-Nina, but recently weakened. The following are links to additional SST information. (note the initial projection) (link 18).

Full disk satellite imagery and other diagnostic monitoring tools show that the Eastern Hemisphere tropical convective forcing has been getting better organized during the last 5-7 days in the region of Indonesia. In general, this region of intense to severe tropical thunderstorm activity, responsible for recent high-impact weather including what was category 3-4 cyclone Nargis, extends from the eastern Bay of Bengal into the southwest Pacific Ocean. There has been some east-northeast drift of this forcing; however, it is generally stationary. Sporadic but at times intense thunderstorm activity continues across portions of tropical South America and especially Africa. No matter what anyone wants to “use”, there is little projection onto a MJO.

The WB (2007, 08) Global Wind Oscillation (GWO), a much better dynamical measure of the atmospheric circulation than, for example, an empirically derived equatorially confined MJO index designed to isolate ~10-20% of tropical rainfall and zonal wind variations (on average), is more appropriate to monitor the current situation. Recall that the GWO considers all tropical convective forcing including the MJO, in addition to red noise extratropical processes.

A well defined orbit in phase space to nearly octant 5 occurred ~23 April (3-day averaged), before collapsing approaching phase 1, updated through 1 May. This trajectory through GWO phase space was expected based on a friction-mountain torque index cycle discussed in my 19 April posting. Recall a week-2 low confidence probabilistic prediction of literally a ferocious USA Great Plains baroclinic storm leading to multiple high-impact weather was offered. The weather events during the past few days speak for themselves.

The forecast discussed above was well before ANY of the models caught on. In fact, the week-2 NCEP GFS ensemble mean forecast had a 500mb height ACC of nearly minus 0.3 for the North American sector this past week (see link below). Also, this prediction was offered well before anything “official”. My point is not to “pat myself on the back”. Past blog postings also speak for themselves of the many poor assessments I have made. However, there is, on average, additional skillful information for making subseasonal predictions based on weather-climate linkage and some understanding of atmospheric dynamics. The models are not stand alone! They are only a component of a forecast process. WB will demonstrate the latter scientifically and objectively once needed resources are given. .

A lot of complex dynamics involving the earth-atmosphere angular momentum budget including the surface torques and transports, as well as Rossby wave energy dispersions (RWDs) “spreading information around”, continue to occur as I type. I want to be as brief as possible in the following.

During the past couple of weeks, the same processes responsible for the recent upward GWO orbit have added anomalous zonal mean westerly wind flow (by definition) to the upper tropospheric tropical and subtropical atmospheres (~3m/s weekly average at 250mb). Much of the latter has come from twin cyclones near the date line and the Western Hemisphere Pacific Ocean. In fact, global relative AAM updated through 1 May per ESRL/PSD R1 data plots show the global integral just barely below climatology. In a sense, the persistent El-Viejo base state has been “dented”. There is evidence from the animations and other tools that this westerly wind flow is propagating poleward (and downward) into both hemispheres. That includes anomalous westerlies across central Asia. As discussed below, I do expect the North Pacific Ocean jet to extend (as a response) during the next couple of weeks.

The GWO is collapsing into phases 1-2, with a global mountain torque of ~minus 10 Hadleys including East Asia contributing. The AAM transport signal showing a strong zonal mean sink around 60N and source near 40N is consistent (in a complicated way) with this. In fact, the higher latitude sink is tied to recent blocking structures including a negative phase of the NAO. The latter has been forced from RWDs tied to Eastern Hemisphere tropical forcing and the recent upward circuit of the GWO discussed above. My point is to show a quick example of the NAO being tied to red noise processes. In other words, this is a response to decay time scale dynamical forcing, and not a cookbook for making subseasonal forecasts (my rottweiler dog from Hell is growling)!

Latest animations of various daily mean vector wind anomaly fields give weak evidence of a zonal wave number 2 pattern of tropical circulation anomalies. However, the most dominate features are the Eastern Hemispheric baroclinic mode consisting of twin tropical upper tropospheric anticyclones near 100E with cyclones near the date line. Zonally oriented chains of anomalies generally dominate the global midlatitudes consistent with the notion of a low AAM base state circumglobal teleconnection (Branstator 2002; there is also a high AAM base state rendition).

Having gone through a lot of details, I do see some evidence that another circuit of the GWO is probable during the next 2-3 weeks. I think it will involve a mountain-frictional torque index cycle and that the GWO orbit will be shifted toward phases 2-4. The tropical convective forcing will be tied to this GWO evolution. It is only a matter of time before the Indian Ocean becomes active. My feeling is during the next few weeks, while the Indian Ocean convection increases, the west central into the South Pacific Ocean will remain active. However, I do not think there will be an abrupt eastward shift of the current Eastern Hemisphere tropical convective forcing toward the date line having a robust WWB, etc. The latter is one behavior needed to “exorcise El-Viejo”.

One or two relatively weak western USA troughs are probable during the next 1-2 weeks. Understanding the seasonal cycle, a much more energetic system, linked to an extended North Pacific Ocean jet, may first slam the USA west coast then the Plains by week-3. Feedbacks from higher latitude blocking (and any west Pacific Ocean convection) will tend to keep the storm track depressed south along with much of the country being cooler than normal at times. Other weather ramifications are much more than obvious by now. However, I will emphasize that another Rockies-Plains high impact weather situation appears probable (above May climatology) during ~ weeks 2-3. At some point perhaps WB can show online GWO composites for forecasters to judge for themselves.

My concerns of prolonged dryness remain for the central and southern High Plains. The latest drought monitor from CPC shows increasingly large areas of severe drought. Unfortunately, another situation of a dry intrusion with high wind and dust greeted portions of western Kansas this past week. I continue to hold out some “hope” for rainfall for these areas. The added subtropical westerly wind flow will help. For example, to reduce the likelihood of USA cold fronts penetrating the deep tropics to as far south as at least the Panama Canal disrupting moisture transport. There were at least 2 occurrences of that during April.

Locations centered on Indonesia including Southeast Asia and the Philippines are likely to get hammered with intense to severe thunderstorm activity week-1, shifting eastward weeks 2-3 into the west central and South Pacific Ocean. While the tropical cyclone hazard for the Bay of Bengal appears diminished, that may not be the case for particularly the northwest Pacific Ocean including the Philippines by weeks 2-3 (could be sooner). Portions of equatorial Africa including the Gulf of Guinea are also getting intense precipitation. As discussed above, that activity may shift east into the Indian Ocean during weeks 2-3. I continue to leave it to the expertise of the appropriate weather centers internationally to alert the public of additional weather hazards worldwide.


An experimental quasi-phase space plot of the GSDM utilizing time series of normalized global relative AAM time tendency (Y-axis) and normalized global relative AAM anomaly (X-axis) can be found at

This phase plot is being re-done, stay tuned. We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous to the WH (2004) “convention”. In addition, the GWO plot does not have the ENSO signal removed.

Please see the revised description of the GSDM per above link. Also, I encourage the readers to study the annotated MJO and GWO phase space plots to help relate the global variations explained by those techniques to “weather”.

Links to CPC and PSD ENSO discussions:

The following is a link to information about the stratosphere and other nice monitoring tools:

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification.

The WB (2007) paper on the GSDM has been published in the February issue of MWR. In addition, a two-part paper is in ACTIVE preparation by WB that will formally introduce the GWO along with subseasonal composites for variables such as surface temperatures. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships.

Given shift work and travel, updates are extremely difficult. I will try to post another discussion next weekend, 10-11 May.

Ed Berry

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