Saturday, June 07, 2008

MJO # 6 (not 666) -- A Witch Doctor?

There is little overall change in the spatial pattern of global SSTs since my last discussion. Anomalous horseshoes of warmth and coolness remain across the Pacific Ocean basin, particularly the Northern Hemisphere. In fact, SST totals greater than 27C extend to 20N at the date line. Other details can be viewed from the links below. (note the initial projection) (link 18).

There are a couple of observations I would like to share. First, per 5-day averaged TAO buoy data, equatorial subsurface anomalies are currently nearly opposite (through 6 June) compared to a year ago. That is, while the equatorial Pacific Ocean thermocline was relatively shallow a year ago, the opposite is now the case. Multiple MJO events since a year ago have contributed, leading to the ~1-3C anomalous warmth from roughly 200m depth west of the date line to 50m deep west of South America. Does this support the notion of transitioning to an equatorial Pacific Ocean warm event?

Continuing, as shown in the SSTA Hovmoller plot per following link,

there has been an approximate biennial character to warm and cold events since 2001-02. For example, note the periodicity of the ~1.5C anomalous warmth in relation to the date line.

However, that behavior appears to have changed since early 2007. Tied to the latest basin wide cooling, the above average warm pool SSTs have shifted to west of 140E on the equator. There are numerous other points that can be raised. Cutting to the chase, based on diagnostic monitoring utilizing various tools, a lot of work involving the coupled ocean-land-atmosphere dynamical system is going to have to be done to shift anomalously warm SSTs into the west central Pacific Ocean by boreal autumn. In the presence of extreme uncertainty (recall my posting last week), a “tilt” toward La-Nina may continue into 2009 (as part of the interannual component of the weather-climate system). Stay tuned.

Full disk satellite imagery shows intense to severe tropical thunderstorm activity extending from the Arabian Sea east-southeast into the extreme west central Pacific Ocean. Tropical rainfall has become generally sporadic elsewhere. The core of what is MJO #6 (since ~October 2007) is ~5-10N/100E, and is not only enhancing the monsoon systems, but also frontal activity across southeast China and eastern Australia. Water vapor imagery shows the polar and subtropical jets extending from this Eastern Hemisphere tropical convection leading to a central Pacific Ocean ridge and another one of those troughs across the western USA (more said below).

Updated through 6 June, WH (2004) phase space plots, particularly with the interannual component left in, indicate a nearly 2 standard deviation MJO projection in phase 3. This coherent evolution of MJO #6 was not captured very well by most statistical and dynamical predictive schemes. There are still predictions of quickly decaying this event, and I do not agree with that. Based on some thoughts of coupled dynamics involving the earth-atmosphere AAM budget, discussion was offered a week-ago that the tropical forcing would remain intact taking on the west-northwest to east southeast orientation across the Eastern Hemisphere discussed above. Those same processes led to a rapid increase of the surface trades (~5-10m/s anomalies) across the central and western Pacific Ocean (was expected), diminishing the tropical cyclone risk in that region. I did not offer a good statement of a decreased northwest Pacific Ocean tropical cyclone hazard a week ago.

I feel quite comfortable where I think the coupled global weather-climate system is at, and where it may be going. Keeping in mind seasonal cycle issues (boreal summer, austral winter), meridional symmetry of zonally symmetric zonal mean circulation anomalies continues. There is strong tropical-extratropical coupling leading now to a Branstator (2002) circumglobal teleconnection of midlatitude ridges. Some of the details of this situation were discussed last week. Even though the WB (2007, 08) GWO projection may appear weak, updated through 5 June there is still an orbit nearly in phase 3, and the above is consistent with a La-Nina base state. As stated previously, this type of circulation response to dynamical processes involving tropical convective forcing and midlatitude mountains has been observed frequently since January 2008 (“the season of the witch”).

Through 5 June, global relative AAM is ~minus 1 standard deviation below the R1 data climatology, with a near zero tendency. There are also relatively weak global signals of the surface torques and zonal mean AAM transports (for now). Hence why the WB (2007, 08) GWO projection is not that robust. However, the latter is a dynamical measure of the global circulation meaning that is it important to pay attention to its evolution. During the last couple of weeks there has been a clustered positive global mountain torque event peaking around 15 Hadleys just before 1 June. That has contributed to the most recent circuit in the WB (2007, 08) GWO phase space centered on octant 3, and a regional response of another anomalously strong North Pacific Ocean jet. Tied to this global mountain torque episode as well as processes linked to the MJO, poleward propagation of zonal mean easterly wind flow anomalies in the subtropical atmospheres (~10-20 N/S) and westerly anomalies in the midlatitudes (~30-40 N/S) has been occurring this past week.

Animations of upper tropospheric daily mean vector wind anomalies continue to present the expected and improving circulation response consistent with the WB (2007, 08) GWO. Twin upper tropospheric tropical anticyclones are becoming established the Indian Ocean with cyclones in the region of the date line. Equatorial westerly wind flow anomalies (~25m/s at 150mb) are increasing east of the date line, part of the baroclinic response linked to the strengthening trades. Rossby wave energy dispersions (RWDs) continue strongly zonally oriented across the midlatitudes, leading to another western USA trough as I type.

I think the Eastern Hemisphere tropical convective forcing will coherently propagate east, with the centroid perhaps reaching the west central and northwest Pacific Ocean weeks 2-3. Last week I speculated a scenario suggestive of a slow evolution toward an equatorial Pacific Ocean warm event. While still in the cards, I am now less confident of that possibility. Again, monitoring within the WB (2007, 08) GWO dynamical weather-climate linkage framework is critical, and cook book techniques will not cut it! I am getting concerned that this latest MJO may be start of a process to rejuvenate a “weaker El-Viejo” which may persist into 2009.

Given the history of the last 5 MJOs, keeping in mind seasonal issues including the Indian/Asian monsoon systems, I think it is probable for a component of coupled tropical forcing to shift into the Western Hemisphere by weeks 3-4. The WB (2007, 08) GWO should circuit into phase 5, then collapse. Hence another strong event of meridional RWD amplification across the PNA sector typical of “WH (2004) MJO phase 8 plus La-Nina” is probable ~late week 2-week 3. The response regionally would be an anomalously deep north-south oriented trough across the western USA. Examples of the latter include ~1 December 2007 and recently ~22-23 May 2008. Both of these situations led to several periods of high impact weather across the Rockies and Plains, and were poorly predicted by the ensemble numerical models at least 11-14 days in advance.

While uncertainty is always there, I disagree with official forecasts stating there is currently not enough information to make probabilistic risk statements of temperature, precipitation, severe local storms, etc. beyond day 10. Relying on the models alone, not only for subseasonal predictions, but even much shorter time scales, is a cookbook and NOT meteorology (insert angry Rottweiler!). Once the work of the WB (2007, 08) GWO comes to maturity that will include tools such as overlapping statistical composites and an objective predictive scheme for the GWO (with hindcasts, etc.), a much more sophisticated evaluation of the numerical models will be possible.

Slowly shifting northwest with the seasonal cycle, ramifications of western USA troughs and a downstream eastern USA ridge are all too familiar. With variations in amplitude, this regional situation for the country appears likely to continue perhaps into early July. The “big event” discussed above may be the last week of this month or first week in July. Again, timing is a white noise deck of cards with the dealer being the Devil. Locations centered on Iowa may not have much relief from additional rounds of destructive severe local storms and flooding rainfall “until further notice”.

As discussed above, portions of the Arabian Sea into India/Indonesia and Southeast Asia/China are likely to be impacted by intense to severe thunderstorms during the next 1-2 weeks. During weeks 3-4 that area of enhanced rainfall may become focused from Southeast Asia into the Philippines and the west central Pacific Ocean. Enhanced rainfall may also appear across portions of Central and South America during weeks 3-4.

Please see the latest statements from the JTWC and TPC for tropical cyclone concerns. A late season tropical hazard may continue week-1 for the Arabian Sea and Bay of Bengal, shifting into the Northwest Pacific Ocean by week-3. The Western Hemisphere may have a less than climatological risk from tropical cyclones weeks 1-2. Other severe/high impact weather has been increasing internationally. I trust the expertise of the appropriate meteorological centers 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, as is the web site. 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:

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, 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. In fact, we are close to submitting part-1. 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 not be able to post another discussion until the weekend of 21-22 June. However, stay tuned for any “quick updates” prior to then.

Ed Berry

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