Edited 18 February to clarify some points.
The spatial pattern of tropical SSTs from
The combination of persistent intense-severe tropical convective rainfall (including tropical cyclones) south of the equator and cold continental air plunging into the North Indian Ocean and
At depth per latest 5-day averaged TAO buoy data recently trade wind intensified cold anomalies of ~minus 3-6C extends to ~150-200m east of 150W with slightly deeper positive anomalies to the west. The latter extend to at least 140-150E with magnitudes ~1-3C, and is the most recent attempt of an oceanic Kelvin wave. In terms of 20C degree isotherm depth, this Kelvin wave is the strongest so far this boreal 2007-08 cold season. Enhanced trades do appear to be weakening it. In any event, the equatorial Pacific Oceanic thermocline remains much steeper than climatology.
Worth repeating from a week ago, there are several modeling and statistical tools suggesting that El-Viejo is not going anywhere anytime soon. For example, please see
http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection).
Also, the WMO has released a nice update dated 11 February on La-Nina, and can be accessed from the following link.
Please remember that MJO tropical convective variability (3 MJOs) has been strong since November 2007 and have acted to constructively and destructively interfere with ocean-atmosphere La-Nina coupling (latter especially in the zonal mean). Specifically, MJO variability is the strongest since at least the 2004-05 boreal cold season, and is atypical of a strong La-Nina. Working within the La-Nina base state, the MJO variability has significantly impacted global weather with numerous occurrences of severe high impact storms. That has included the
Full disk satellite imagery and other tools show the strongest moist tropical convective forcing centered ~10S/130E while still extending from eastern
Existing circulation and SST anomalies tied to La-Nina coupling along with atmospheric responses from the previous 2 MJOs appear to be affecting the behavior of the current one. For instance, since early this month a westward shifting component along the equator weakly projecting onto a Rossby mode per Wheeler and Kiladis (JAS 1999; WK(1999)) coherent modes Hovmollers has been present. Interactions with the northern extratropics may have also contributed to the westward shift. In any case, well south of the equator (need to remember the seasonal cycle) from northern
My point is evaluation of any MJO must consider other fields such as the SSTs, tropospheric wind structures, etc., in addition to regions of precipitation enhancement and suppression. Besides the seasonal cycle, propagation of this current MJO is south of the equator because of the cold El-Viejo SSTs in the region of the equatorial date line. I do think a difference between our current MJO and the previous event (MJO #2) is that it is less probable for extremely intense convection to persist (~2 weeks) across the South Pacific Ocean. The SSTs in that region are certainly warm enough to support tropical convection (and are), ~28-29.C, but not 30-31C like that seen during mid-January.
This MJO already has significantly impacted and is probable to continue impacting the
A week ago discussion was given about our global circulation exhibiting zonally symmetric zonal mean zonal wind anomalies meridionally symmetric about the equator. I will not repeat all that here. There is some evidence from animations of upper tropospheric daily mean vector wind anomalies that the zonal symmetry may be changing. I want to keep the elaboration that follows as brief as possible (a properly dedicated web page effort would greatly facilitate communication and understanding).
Well defined twin tropical/subtropical anticyclones (wind flow anomalies ~20-30m/s at 150mb including cross-equatorial flow) are present ~160E tied to MJO #3 (16 February), and continue to steadily move east. Downstream cyclones also with large wind flow anomalies exists ~160W. Consistent with phases 7-8 of the DJF MJO composites produced by Weickmann (paper by WB in preparation), strong meridional Rossby wave energy dispersions (RWDs) arc from the anticyclones across the PNA sector leading to anomalous ridge across western Canada. In fact, this is (ONLY) one reason why the short-term global models have struggled with the evolution of the baroclinic storm on the USA Plains that is about to develop (at the time of this writing on 16 February). The latter serves as yet another example why an understanding of the dynamics of slower evolving large-scale processes needs to part of any forecast process for making predictions for days 1-7. Weather and climate are linked and using numerical models as a stand alone forecast tool is another cookbook technique. All the statistical model bias correction in the world is not a scientifically acceptable solution!
The global atmospheric AAM budget remains non-trivial. Loosely, there are competing dynamical processes wanting to both add and remove westerly wind flow from the atmosphere. Perhaps we are observing a La-Nina equilibrium in terms of the earth-atmosphere angular momentum budget. Updated through 14 February courtesy of ESRL/PSD, global AAM is slightly below the R1 data climatology with the tendency ~minus 10-20 Hadleys. That is why the Global Wind Oscillation (GWO) is orbiting in phase space toward phase 2. However, zonal mean zonal wind anomalies remain very strong (at least ~5-10m/s at 200mb), with equatorial westerlies, easterly wind flow anomalies dominating the subtropical atmospheres (propagating south in the Northern Hemisphere) and westerly anomalies across the Southern Hemisphere extratropics. However, zonal mean easterly wind flow anomalies have recently appeared ~50N. So, what could be going on?
Recall last week I talked about the East Asian mountain torque remaining persistently positive since ~mid January having roughly 10 day variations. This apparently started as a feedback to west central and
RWDs arcing from the western
Reading the above brings back memories of the recent “storm on steroids” that severely impacted the
Animations of various wind fields and several tools clearly tell me that upper tropospheric divergence is increasing across tropical South America (per above) and will soon do so across
Finally, for those who watch the stratosphere, as discussed above, there have been numerous RWDs leading to bursting anticyclones across the Northern Hemisphere polar latitudes. Another such event is currently in progress, and at least a minor warming may occur. Upward directed 100mb zonal mean E-P fluxes around 60N have become quite robust during the past week. It is not unusual to see a major SSW going into March, which can then impact the troposphere by raising sea-level pressures across the
Summarizing, the MJO dynamical signal is moving into the
Most, if not all models (ensembles), have now captured the notion of the
Troughs then moving into the Rockies leading to an intense southwest flow storm track across the central
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 will leave it to the expertise of the appropriate weather centers internationally to alert the public of these risks.
Tropical cyclone activity should diminish week-1 across the South Indian Ocean and northwest coasts of
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. I will attempt another posting the weekend of 23-24 February.