Friday, June 20, 2008

ENSO Neutral with Lingering La-Nina Circulation?

The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”

Global tropical SST anomalies are relatively weak. Exceptions include the cool anomalies in the region of the equatorial date line, and warmth across the equatorial East Pacific as well as the central and eastern tropical Atlantic Oceans (from arguably an Atlantic El-Nino that matured during boreal spring). Anomaly magnitudes for the latter are ~1-2C. Warmest SSTs are still from the central Indian Ocean into the tropical Northwest Pacific basin with totals ~28-30C. Outside the tropics, the warm and cool horseshoe anomalies across the entire Pacific Ocean basin having the spatial pattern typical of El-Viejo remain well defined (I am well aware of the PDO “fans”).

Subsurface anomalies and everything else that can be argued about all understood, I offer the following. Remembering that ENSO is only a component of an interannual signal involving the global coupled ocean-land-atmosphere dynamical system, I think it is more likely to see some rejuvenation La-Nina than an evolution toward El-Nino going into boreal winter 2008-09. However, uncertainty is very high. Stay tuned. The following are links to additional SST related information. (note the initial projection) (link 18).

In general, subseasonal signals as given by the WH (2004) MJO and WB (2007, 08) GWO phase space plots are weak. In fact, the WH (2004) projection is near zero, even with the interannual component left in. While generally true that subseasonal signals are currently fairly weak, there is still information to be gained from careful thought and diagnostic monitoring, as well as having an understanding of how the phase space plots are derived. Also, I disagree with any notions (official or otherwise) that useful predictive probability statements of any possible high impact weather (etc.) cannot be made in these “weak” situations (my Rottweiler is growling -- wanted to work him in!).

Full disk satellite imagery and other tools loosely suggest 2 regions of enhanced tropical convective forcing across the Eastern Hemisphere. One region is centered on the Indian Ocean from the equator into the monsoon systems with the other focused on the west central Pacific Ocean ~0/145E. The former has been slowly weakening with the latter intensifying, including Typhoon Fengshen hammering the Philippines. West Pacific tropical cyclone development was offered as a possibility in my posting about 2 weeks ago.

I feel comfortable defending the notion that Rossby wave energy dispersions (RWDs) tied to the Indian Ocean forcing interacting with the extratropics (and vice-versa) led to the west central Pacific Ocean signal. For example, there was enhancement of the upper tropospheric twin tropical cyclones near the date line leading to intensified divergence across the west Pacific Ocean. In addition, equatorial westerly wind anomalies of ~25m/s at times have also occurred with the twin cyclones. These westerly anomalies are shifting poleward (in a manner too complicated to discuss here) and are/will impact the extratropics in the near future (more said below).

Global relative AAM (only updated through 16 June; data issues again) remains a good 1 sigma below the R1 data climatology. A recent spike in the global mountain torque (~plus 25 Hadleys) having the largest contribution from East Asia is why the WB (2007, 08) GWO shows a circuit toward octal 5. This positive mountain torque event also contributed to the intensification of the west central Pacific Ocean tropical convection discussed above (and added westerly wind flow anomalies to the atmosphere). Animations of mean sea-level pressure anomalies suggest this component of the global mountain torque is decreasing.

Continuing, while the recent computed AAM tendency may be relatively large (3-day average), the calculated AAM tendency is near zero. Reasons include a negative Coriolis torque and fairly weak zonal mean AAM transports. In any case, the WB (2007, 08) GWO is more likely shifted toward octant 3 but having fairly fast orbits in phase space.

As discussed above, there is evidence of westerly wind flow anomalies shifting into the subtropical atmospheres, flanked by poleward propagation of zonal mean easterly wind flow anomalies through the midlatitudes. Thus animations of daily mean upper tropospheric vector wind anomalies do suggest a return of a circumglobal teleconnection of midlatitude ridges. Midlatitude RWDs are generally zonally oriented, anchored by twin tropical/subtropical anticyclones in the region of the Indian Ocean and cyclones around the date line. Overall, with robust zonal mean westerly wind flow anomalies present at the higher latitudes (~15-20m/s at 200mb ~60S), once again there is some meridional symmetry of zonally symmetric zonal mean circulation anomalies.

So, where does the atmosphere go from here? First, I think there will be a tropical convective forcing signal propagating fairly quickly through the Western Hemisphere during the next 1-3 weeks. In fact, a zonal wave number 2 structure of tropical circulation anomalies may again emerge. The Eastern Hemisphere monsoon systems may have a break, but perhaps only briefly for various reasons.

The RWDs are one of the mechanisms bringing anomalous subtropical westerly wind flow into the midlatitudes. Cutting to the chase for the PNA sector (remembering boreal summer), a strengthening of the jet across the North Pacific Ocean collapsing into an anomalous northwestern/western USA trough by around week-2 I think is probable. At some point ~weeks 3-4 that trough (made up of synoptic events) is likely to shift east. Numerical models have been trending toward the latter for week-2.

A source of uncertainty but critical for the severe storms/flood ravaged areas centered on Iowa is how far south will the jet extend going into July? My own feeling is enough for rounds of intense-severe MCS activity starting week-2 (week-1 understood). Other locations across the central Plains into the Mississippi Valley are probable for at least climatology MCS activity. Areas that have been dry will hopefully receive beneficial rainfall. While portions of the northwestern states tilt toward cooler than normal, intense heat initially across the Desert Southwest and southern Plains may expand into the Deep South, Ohio Valley and portions of the East Coast weeks 2-4.

Per above, the monsoon systems of India and Southeast Asia may have lessened rainfall intensity ~weeks 1-2 compared to the last couple weeks while the west central and northwest Pacific Ocean remains active at least week-1. Intense to severe thunderstorm activity including additional tropical cyclones is a concern for the latter including the Philippines. By weeks 2-3 rainfall may become quite intense from the East Pacific Ocean ITCZ all the way into equatorial Africa. Please see the latest statements from the JTWC and TPC for tropical cyclone concerns. There may be an increased risk for tropical cyclone development across the East Pacific starting week2 and perhaps the Atlantic basin by weeks 3-4.

Other severe/high impact weather continues internationally. I trust the expertise of the appropriate weather 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. This web page effort would hopefully include an objective predictive scheme for the GWO, including hindcasts.

The WB (2007) paper on the GSDM has been published in the February issue of MWR. In addition, the first of a two-part paper has been submitted to MWR where WB formally introduces the GWO, including the "correct" rendition of the GWO phase space plot. A pdf version can be downloaded from the following link

Overlapping seasonally varying subseasonal composites for variables such as surface temperatures and streamfunction anomalies are planned on being presented in part-2. 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 frame work to evaluate the numerical models in a sophisticated manner as part of a subseasonal (and any time scale) forecast process. Relying on the numerical models alone is a cookbook!

Given shift work and travel, updates are extremely difficult. I hope to post another discussion the weekend of 28-29 June.

Ed Berry

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