The weather-climate situation has generally evolved as expected per my discussion a week ago and I would like to avoid repetition for brevity. The purpose of this writing is simply an update.
Mature La-Nina conditions continue across the
The following are links for additional SST information:
http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)
http://www.wmo.ch/pages/prog/wcp/wcasp/enso_update_latest.html (getting dated).
The tropical convective forcing continues to slowly organize across the
Various predictions of the MJO in WH (2004) phase space from worldwide weather centers suggest a strong signal to emerge in roughly the central
The global circulation has been responding to the tropical forcing as well as to other dynamical processes explained by the GWO. Animations of upper tropospheric daily mean vector wind anomalies show twin tropical/subtropical anticyclones centered ~110E becoming better defined with cyclones just east of the date line.
The most dominate subseasonal atmospheric signal is currently the GWO (in contrast to the weak MJO), strongly in phase 2 updated through 28 February (more said below). Processes that define the GWO (which includes the MJO) such as AAM transports and surface torques is why recently most Rossby wave energy dispersions (RWDs) have been zonally oriented. With the retraction of the East Asian jet during the past week (tied to the Eastern Hemisphere tropical forcing), there has still been Rossby wave energy dispersed (rather than trapped) along poleward directed ray paths across both the North and South Pacific Oceans. The Northern Hemisphere RWD links up to the trough currently digging across the western
Global relative AAM is a good 2 AMUs (roughly 2 standard deviations) below the R1 data climatology updated through 28 February. This is the lowest since early December 2007 and already demonstrates that tropical forcing including what is likely to be MJO #4 is amplifying La-Nina. Global relative AAM during the past 12 months was lowest on about mid August, dipping close to 4 AMUs below the R1 data climatology. Interesting that last August was also the month that the global financial markets started having their problems, which still continue. The global AAM tendency is still ~minus 20 Hadleys with components such as the earth AAM tendency and frictional torque contributing. The latter is roughly minus 15 Hadleys mostly from surface frictional dissipation of midlatitude westerly wind flow anomalies that I can easily link to the MJO tropical variability.
The global mountain torque is slightly negative; however, the East Asian component remains slightly positive. The East Asian mountain torque has been generally positive since mid January, providing a local source of midlatitude westerly wind flow for features such as the East Asian/North Pacific Ocean jet. There have been roughly 10-20 day variations of this torque, and I can offer some attribution for it. The point is this local source of westerly wind flow may have been keeping the position of the PNA midlatitude ridge, on average, closer to the North American west coast since then.
Zonal mean easterly wind flow anomalies strongly dominate the subtropical atmospheres, with magnitudes still ~10-15m/s at 200mb for the Northern Hemisphere. Following the zonal mean AAM tendency, after an extended period of Northern Hemisphere equatorward propagation, the anomalous easterlies are again shifting off the equator. Anomalous zonal mean westerly wind flow is present across the midlatitudes. Particularly for the Northern Hemisphere, consistent with this meridional symmetry there is decent zonal mean signal of poleward AAM transport ~30-35N given a subtropical sink and a midlatitude source.
The GWO is arguably the strongest in phase 2 (of phase space) since early December 2007. During the next few weeks as MJO #4 starts to propagate east toward the west central Pacific Ocean, working with other processes westerly wind flow is probable to be added to the subtropical atmospheres. Thus I remain unchanged about my prediction for the GWO to orbit through at least phases 3-5 (legacy WB (2007) GSDM Stages 1-2) which may really “anger” La-Nina.
Yes, there has been a recent major warming in the Northern Hemisphere polar stratosphere. Including the at least 3 minor warmings before that, I can link these events to MJO and other forms of complex variability. Zonal mean 100mb full field vertical EP fluxes are now downward meaning impacts from this warming are impacting the upper troposphere. In fact, in the region of 75N zonal mean easterly wind flow anomalies at 50mb are ~20-30m/s while at 200mb ~10m/s. An astute reader will also observe a zonal mean AAM sink ~60-70N. This all suggests an increased probability of higher latitude blocking along with anomalously high mean sea level pressures for the next few weeks. Carrying on, that can lead to a southward shifted midlatitude storm track.
Climatologically, it is not all that unusual to see the troposphere respond to the stratosphere as discussed above going into boreal spring. In fact, per zonal mean sections of 50mb wind the final stratospheric warming usually occurs by the end of April. Whether or not we are seeing this event early or whatever is unclear. This is nothing more than a dynamical feedback to slow processes including subseasonal atmospheric variations which can be monitored within the GSDM framework. Perhaps this line of thought also adds to the many other reasons why several locations across the
Summarizing, another atypical subseasonal enhancement of La-Nina is probable during the next few weeks. Both the GWO and MJO may be approximately in the same phases. Most, if not all, week-2 ensemble means from international weather centers of say, 500mb geopotential height anomalies, give a prediction of a western North American ridge-eastern trough. While I do know where that is coming from, those predictions are misleading since they are weekly means. It would “surprise me” not to see another onslaught of western
Probable weather impacts for the
Still unchanged, 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 continue to leave it to the expertise of the appropriate weather centers internationally to alert the public of these risks.
Locations from the eastern Indian Ocean through
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. Given shift work and upcoming travel, updates will be difficult. I will try to issue at least a short posting next weekend.