Warmer than normal waters having similar anomalies as their La-Nina counterpart prevail generally along and south of the equator from the Indian Ocean-northwest Australia. SST totals in this region are ~29-30C. There is still the well-pronounced warm SST anomaly horseshoe extending from the far equatorial west Pacific Ocean into especially the Northern Hemisphere. Finally, responding to a recent westerly wind burst south of the equator, positive anomalies (5-day mean) in excess of 4C have developed ~200m at 165E. Together with the cold anomalies farther east, this is a strong signal of a steeper than normal equatorial oceanic thermocline, typical of La-Nina. Whether or not a coherent oceanic Kelvin wave gets (or already is) generated is unclear.
Full-disk satellite imagery and other diagnostic monitoring tools indicate renewed strong-severe tropical convective forcing from South Africa-central equatorial
MJO tropical variability thus far has been the strongest since the boreal 2004-05 cold season, and this is unusual for a strong La-Nina such as the one currently in progress. Whether or not the start of MJO#3 for the boreal 2007-08 is in progress remains unclear. However, the west central-South
As was the case for MJOs #1-2 constructively and destructively interfering with our La-Nina base state, the redevelopment of Indian Ocean tropical forcing is probable to enhance/amplify it. Keep in mind that dynamical processes in the atmosphere cannot be “shoe-horned” into simple "recipes". For example, it is not accurate to attribute the intense USA west coast winter storm ~3-4 January 2008 simply to the MJO. In reality the moist MJO tropical convective forcing centered on Indonesia amplified an already existing La-Nina base state allowing a cold trough to slam the west coast. There is no short cut to understanding the dynamics of physical atmospheric processes involving forcing-response-feedback-subsequent interactions impacting multiple time and space scales. The latter is important if we are to improve to making predictions of especially, for instance, high impact weather events weeks 1-3. Numerical models will struggle when there are rapid and complex changes involving tropical convective forcing with subsequent extratropical interactions, no matter how much bias correction is employed.
Since early-mid December 2007, responding to MJO#2, well defined poleward propagation of zonal mean easterly wind flow anomalies occurred from the equatorial into the subtropical/mid-latitude atmospheres of both hemispheres. Currently there are westerly wind flow anomalies shifting off the equator into the subtropics, particularly the Northern Hemisphere (~10m/s at 200mb). That is why there are several low-latitude closed lows with subtropical jets, globally.
With the added subtropical westerly wind flow from the last MJO, global relative AAM continues to hang around ~minus 1 standard deviation below the R1 data climatology through 23 January. Also helping to keep global AAM from plunging like the financial markets have done so far this year is a ~10-15 Hadley positive frictional torque. The latter is a direct response to the poleward and downward propagation of the zonal mean easterly wind flow anomalies discussed above, especially to around 20-40N (weaker ~15-30S).
A strong zonal mean poleward AAM transport signal has appeared ~50N while weakly equatorward ~20N, meaning midlatitude split flows that have regionally been across the oceans and roughly central
Also updated through 23 January, the GWO signal has orbited weakly to phases 4-5 in the daily mean. I suspect the orbit will shift a bit toward the left into the region of phase 3 (old GSDM Stage 1 – “La-Nina attractor”) during the next week or so. In fact, supportive of this notion, animations of upper tropospheric daily mean vector wind anomalies from ESRL/PSD already show twin tropical anticyclones developing across the
Summarizing, it is still unclear whether or not MJO #3 is developing across the
In the longer term, poleward shifting zonal mean easterly wind flow anomalies do increase the probability of anomalous midlatitude ridges. Where these ridges become established obviously has a lot to do where drought may occur say, for this upcoming boreal summer. Right now, that is unclear. Hence statements about possible drought centered on Iowa this upcoming warm season are very much premature. In fact, I can easily speculate an opposite scenario.
Internationally, a significant tropical cyclone risk exists from
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 t0 WH(2004) “convention”. In addition, the GWO plot does not have the ENSO signal removed.
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. Work is on-going by Weickmann and Berry to submit a paper that will formally introduce the GWO. I will attempt another posting the weekend of 2-3 February.