Saturday, March 01, 2008

Global Relative AAM and Financial Markets in Sync

The weather-climate situation has generally evolved as expected per my discussion a week ago and I would like to avoid repetition for brevity. The purpose of this writing is simply an update.

Mature La-Nina conditions continue across the Indo-Pacific Ocean sector and this El-Viejo is not going anywhere anytime soon (warming SSTs west of South America understood). Warmest SSTs globally are still across the South Pacific Ocean having totals ~29-30C, a bit cooler than a week ago due to intense thunderstorm activity along the SPCZ. SST totals across much of the Indian Ocean are ~28-29C. We are getting to the time of the year when SSTs are climatologically the warmest across the equatorial Pacific Ocean meaning 5-day averaged (TAO buoy data) negative anomaly magnitudes ~1-3C (totals ~24-27C) are significant. The equatorial Pacific Ocean thermocline remains anomalously steep, and our latest oceanic Kelvin wave appears to be fading due to increased trades.

The following are links for additional SST information: (note the initial projection) (link 18) (getting dated).

The tropical convective forcing continues to slowly organize across the Eastern Hemisphere, loosely centered ~ 0/100E per full disk satellite imagery and all the other tools I can list. Enhanced tropical rainfall is also present across portions of tropical South America and Africa. I think the early developmental stages of MJO #4 are in progress. Per WH (2004) methodology there is little MJO projection.

Various predictions of the MJO in WH (2004) phase space from worldwide weather centers suggest a strong signal to emerge in roughly the central Indian Ocean (phase 2) by week-2. Having my own reasons, I agree with this notion; however, I think the MJO signal will be farther east by week-2 in the region of the East Indian Ocean to Indonesia (phases 3-4). Persistence of tropical forcing from the west central-South Pacific Ocean of the magnitude seen during January is now looking less probable (at least until MJO #4 comes out).

The global circulation has been responding to the tropical forcing as well as to other dynamical processes explained by the GWO. Animations of upper tropospheric daily mean vector wind anomalies show twin tropical/subtropical anticyclones centered ~110E becoming better defined with cyclones just east of the date line.

The most dominate subseasonal atmospheric signal is currently the GWO (in contrast to the weak MJO), strongly in phase 2 updated through 28 February (more said below). Processes that define the GWO (which includes the MJO) such as AAM transports and surface torques is why recently most Rossby wave energy dispersions (RWDs) have been zonally oriented. With the retraction of the East Asian jet during the past week (tied to the Eastern Hemisphere tropical forcing), there has still been Rossby wave energy dispersed (rather than trapped) along poleward directed ray paths across both the North and South Pacific Oceans. The Northern Hemisphere RWD links up to the trough currently digging across the western USA (1 March). Most operational models have been “playing catch-up” to this synoptic event, trending slower and deeper for the last several days. Hence yet another example of the linkage of weather and climate, and why numerical models cannot be used as a stand alone forecast tool without consideration of the global circulation even for the first few days of week-1.

Global relative AAM is a good 2 AMUs (roughly 2 standard deviations) below the R1 data climatology updated through 28 February. This is the lowest since early December 2007 and already demonstrates that tropical forcing including what is likely to be MJO #4 is amplifying La-Nina. Global relative AAM during the past 12 months was lowest on about mid August, dipping close to 4 AMUs below the R1 data climatology. Interesting that last August was also the month that the global financial markets started having their problems, which still continue. The global AAM tendency is still ~minus 20 Hadleys with components such as the earth AAM tendency and frictional torque contributing. The latter is roughly minus 15 Hadleys mostly from surface frictional dissipation of midlatitude westerly wind flow anomalies that I can easily link to the MJO tropical variability.

The global mountain torque is slightly negative; however, the East Asian component remains slightly positive. The East Asian mountain torque has been generally positive since mid January, providing a local source of midlatitude westerly wind flow for features such as the East Asian/North Pacific Ocean jet. There have been roughly 10-20 day variations of this torque, and I can offer some attribution for it. The point is this local source of westerly wind flow may have been keeping the position of the PNA midlatitude ridge, on average, closer to the North American west coast since then.

Zonal mean easterly wind flow anomalies strongly dominate the subtropical atmospheres, with magnitudes still ~10-15m/s at 200mb for the Northern Hemisphere. Following the zonal mean AAM tendency, after an extended period of Northern Hemisphere equatorward propagation, the anomalous easterlies are again shifting off the equator. Anomalous zonal mean westerly wind flow is present across the midlatitudes. Particularly for the Northern Hemisphere, consistent with this meridional symmetry there is decent zonal mean signal of poleward AAM transport ~30-35N given a subtropical sink and a midlatitude source.

The GWO is arguably the strongest in phase 2 (of phase space) since early December 2007. During the next few weeks as MJO #4 starts to propagate east toward the west central Pacific Ocean, working with other processes westerly wind flow is probable to be added to the subtropical atmospheres. Thus I remain unchanged about my prediction for the GWO to orbit through at least phases 3-5 (legacy WB (2007) GSDM Stages 1-2) which may really “anger” La-Nina.

Yes, there has been a recent major warming in the Northern Hemisphere polar stratosphere. Including the at least 3 minor warmings before that, I can link these events to MJO and other forms of complex variability. Zonal mean 100mb full field vertical EP fluxes are now downward meaning impacts from this warming are impacting the upper troposphere. In fact, in the region of 75N zonal mean easterly wind flow anomalies at 50mb are ~20-30m/s while at 200mb ~10m/s. An astute reader will also observe a zonal mean AAM sink ~60-70N. This all suggests an increased probability of higher latitude blocking along with anomalously high mean sea level pressures for the next few weeks. Carrying on, that can lead to a southward shifted midlatitude storm track.

Climatologically, it is not all that unusual to see the troposphere respond to the stratosphere as discussed above going into boreal spring. In fact, per zonal mean sections of 50mb wind the final stratospheric warming usually occurs by the end of April. Whether or not we are seeing this event early or whatever is unclear. This is nothing more than a dynamical feedback to slow processes including subseasonal atmospheric variations which can be monitored within the GSDM framework. Perhaps this line of thought also adds to the many other reasons why several locations across the USA have March climatologically as their snowiest month. Please see the following link for additional stratosphere details.

Summarizing, another atypical subseasonal enhancement of La-Nina is probable during the next few weeks. Both the GWO and MJO may be approximately in the same phases. Most, if not all, week-2 ensemble means from international weather centers of say, 500mb geopotential height anomalies, give a prediction of a western North American ridge-eastern trough. While I do know where that is coming from, those predictions are misleading since they are weekly means. It would “surprise me” not to see another onslaught of western USA troughs by the end of week-2 continuing at least into week-3 (timing is white noise; usual disclaimer). The following outlook is essentially a repeat from a week ago.

Probable weather impacts for the USA ~later week-2 into at least week-3 with more western states troughs should be easily apparent by now. Weeks 4-5 may see an eastward shift of this regime linked to GWO phases 5-7. This may literally be “the season of the witch! (recall La-Nina means little girl; El-Viejo means anti-Christ, etc.).” Already stated above, higher latitude blocking may shift the storm track a bit south at times. Locations such as the Upper Mississippi Valley hit hard by severe winter weather may not only experience more of it, but also have “spring” delayed. The track of what may be violent outbreaks of severe local storms is probable to shift northwest into the northern and central Plains/Upper Mississippi Valley going into May and June.

Still unchanged, per WMO and other information, quite a bit of severe weather internationally continues to occur, tied to our on-going complicated weather-climate situation. I continue to leave it to the expertise of the appropriate weather centers internationally to alert the public of these risks.

Locations from the eastern Indian Ocean through Indonesia, northern Australia and the Philippines are probable to get hammered with intense-severe thunderstorms/flooding rainfall for at least the next 1-3 weeks. That does include a tropical cyclone risk south of the equator. A slow eastward shift is probable as MJO #4 emerges. Hopefully eastern Brasil and portions of central and south Africa will see less intense thunderstorm activity after week-1. At least for the next week or so, the paradise islands of the South Pacific Ocean are not “out of the woods” for episodes of intense/severe frontal thunderstorm activity.


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

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:

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 paper is in preparation by WB that will formally introduce the GWO. Given shift work and upcoming travel, updates will be difficult. I will try to issue at least a short posting next weekend.

Ed Berry

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