The spatial distribution of global SSTs still includes weakening but persistent below normal waters along the equatorial
Needless to say careful detailed rigorous daily monitoring is a must as part of any forecast process to gain some understanding on the future of El-Viejo. There are a couple of outlier statistical and dynamical models suggesting El-Nino SSTs by boreal winter 2008-09. Whatever the case, confidence in any objective predictive scheme must be very low right now, and remember that SSTs from other basins including the tropical Indian and
http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)
In the spirit of brevity, full disk satellite imagery and other diagnostic monitoring tools indicate that the tropical convective forcing across the central and eastern equatorial
Global relative AAM, updated through 17 April per ESRL/PSD, is roughly 2.5 sigma below the R1 data climatology. Not only is the global circulation in our familiar low AAM base state, there is evidence of (again) merdional symmetry of zonally symmetric zonal mean wind flow anomalies (vertically and zonally integrated for the latter). That is, weak equatorial zonal mean anomalous westerlies flanked by zonal mean easterly wind flow anomalies across the subtropical atmospheres. The greatest subtropical zonal mean easterly wind flow anomalies persist across the Northern Hemisphere, having magnitudes ~10-15m/s at 200mb. Westerly wind flow anomalies are present across the mid and higher latitudes; again, particularly the North Hemisphere. That is why anomalous ridges are present across the midlatitudes (as seen in the earth component of the angular momentum budget) leading to anomalous poleward shifted storm tracks, in the zonal mean.
Various animations of several wind fields show that the zonal mean equatorial westerly wind flow anomalies are largely coming from the upper troposphere of the Western Hemisphere Pacific Ocean. The latter is part of the expected baroclinic response to the
The WB (2007, 08) GWO, which is a much better quantitative measure of the global circulation than an equatorially confined empirical MJO index in our current situation, has orbited to a roughly 2 sigma phase 4 projection. The global tendency of relative AAM is ~plus 25 Hadleys which not only has had a contribution from the tropical forcing, but also a recent spike in the global frictional torque of ~plus 20 Hadleys. This strong positive frictional torque has been forced by anomalous surface easterlies from the strong midlatitude ridges discussed above. The point to all this is we have another example of tropical-extratropical coupling, observed so often this past cold season. The WB (2007, 08) GWO can tell us a lot about the dynamics of the non-linear complicated forcing-response-feedback relationships involved.
The punch line to this posting is because of all the scientific issues discussed above (and those I left out), zonally oriented Rossby wave energy dispersions (RWDs) continue to be favored in our current base state (due to trapping of baroclinic energy in the jets). This has been the case since at least November 2007, with a few exceptions such as ~1 December 2007 and earlier this month. As discussed in my last posting, most numerical model predictions failed badly on the latter (see link below as an example).
The zonally oriented chains of circulation anomalies responding to the RWDs not only favor a central
The circumglobal teleconnection pattern is currently present, and has been for roughly the last week. Where the atmosphere goes during the next few weeks will depend a lot on whether or not the Eastern Hemisphere tropical forcing comes out into the west central
A relatively repeatable pattern of troughs coming into the western
I do want to make “special mention” of anomalous cold Arctic air that has been building up in western
My concerns of prolonged dryness remain for the central and southern High Plains. The faster time scales scenario discussed above would be more favorable for precipitation in these areas, as would any eastward shift of tropical forcing into the west central
Locations from the Indian Ocean into at least western
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:
The following is a link to information about the stratosphere:
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 preparation by WB that will formally introduce the GWO along with subseasonal composites. Given shift work and upcoming travel, updates remain extremely difficult. I will try to post another discussion next weekend, 26-27 April.