Warning: Beaten Down El-Viejo Circulation Getting another Injection

Mature and strong La-Nina SST conditions continue across the tropical Indo-Pacific Ocean sectors with no significant changes since my discussion a week ago. There has been cooling north of Australia and warming across the equatorial Indian Ocean, with anomaly magnitudes ~1-2C. The latter is consistent with the locations of enhanced and suppressed tropical convective rainfall, respectively. The warmest SSTs globally are across the tropical South Pacific Ocean having totals ~29-31C, while those across the Indian Ocean are ~28C.

Per latest 5-day averaged TAO buoy data, the equatorial Pacific Oceanic thermocline remains very steep, with negative SST anomalies ~minus 3-5C down to about 150m deep east of 150W. West of the date line positive anomalies ~plus 3C exist down to ~200m depth. Strong trades (anomalies ~5-10m/s) along the equator from ~140W to the warm pool appear to be dampening the oceanic Kelvin wave discussed in my previous posting. The following are links for additional SST information.

http://www.pmel.noaa.gov/tao/jsdisplay/

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

Many scientific issues have been raised in regard to our on-going strong cold event during the past several weeks. These have included the strong MJO tropical convective variability and zonally symmetric zonal mean zonal wind anomalies meridionally symmetric about the equator. I am not going to repeat that here. However, an important point to remember is that the characteristics all El-Ninos and La-Ninas are different (trend signals understood). Composite signals, by definition, are going to average out what many others may consider as “climatic noise”. This is why the dynamics of the subseasonal aspects of cold, warm, and whatever other shoe-horned termed events are extremely important to monitor and understand in real-time. The latter contribute to high-impact weather that often does not fit the composites (and impact the seasonal mean). Weather and climate are linked, and one of the purposes of the GSDM is to provide a framework of that linkage for monitoring and predictions.

Full disk satellite imagery and other tools suggest that the MJO signal has become a bit less coherent, and that there are currently multiple regions of moist tropical convective forcing. The most intense region globally of strong-severe tropical convection is still back in the Eastern Hemisphere centered ~120E just south of the equator. The latter has been slowly expanding west into the South Indian Ocean while still affecting the Philippines to northern Australia with flooding rainfall. Weaker regions of moist convection are across the South Pacific Ocean, tropical South America and even South Africa.

WH (2004) phase space plots now give a less than 1 standard deviation projection in phase 8 (removing the ENSO signal). Whatever the case, animations of upper tropospheric winds and velocity potential indicate that the dynamical signal of the MJO is in the Western Hemisphere. My own loose back of the envelope calculation from a Hovmoller plot of equatorial velocity potential has the signal propagating east ~15m/s. It is typical at this phase of the MJO to see multiple regions of enhanced tropical convection. I continue to lean toward the MJO WH (2004) RMM phase space predictions provided by centers such as CMC, UKMET and ECMWF. These suggest that the convective signal will strongly return to the Indian Ocean by late week-2 and week-3 along with suppression across the Western Hemisphere. I do not expect intense convection to persist across the somewhat cooler waters (compared to 4-6 weeks ago) of the South Pacific Ocean like that observed during mid-January.

Identifying important circulation features from animations of upper tropospheric daily mean vector wind anomalies is not as clear as a week ago. Briefly, the twin subtropical anticyclones with the current MJO have weakened considerably (if not completely dispersed) across the Western Hemisphere Pacific Ocean. Furthermore, consistent more with the GWO (discussed below), Rossby wave energy dispersions (RWDs) have become more zonally oriented during the last few days which are propagating along waveguides too complicated to discuss here.

There is still a signal of merdionally oriented RWDs arcing from the central Pacific Ocean to the anomalous (but weakening) anticyclone across Canada continuing across the North Atlantic Ocean to a large anomalous cyclonic gyre across western Asia. The latter RWD path may play a role in both re-firing Indian Ocean tropical convection (Southern Hemisphere symmetry understood) and finally force the East Asian mountain torque to become negative. The positive East Asian mountain torque has been providing a local source of atmospheric westerly wind flow for the past several weeks, including the recent extension of the North Pacific Ocean combined jet.

The earth-atmosphere angular momentum budget (AAM), which provides extremely useful diagnostic information about the real-time global and zonal mean circulation, remains more complicated than I would like. However, signals are clearer to me than a week ago, particularly taking into account all the above. Furthermore, I am actually fairly confident where the global circulation is headed during at least the next 2-3 weeks.

The screaming message is that dynamical processes are once again increasing zonal mean easterly wind flow anomalies throughout the tropical and subtropical atmospheres, especially north of the equator. In fact, since mid-late January strong zonal mean easterly wind anomalies (a good 10m/s at 200mb) have been shifting south from ~40N to 25N as a response. Prior to that, since early December 2007, there was the more typical poleward propagation. Why the recent southward shifts of the easterly wind flow anomalies is a good question, and I do have my thoughts. I will just offer here speculation that this all goes back to the RWD feedbacks from the South Pacific Ocean signal with MJO #2 including the role of positive East Asian mountain torque.

With surface frictional dissipation of extratropical westerly wind flow anomalies by the synoptic eddies (global frictional torque ~minus 10 Hadleys), updated through 21 February per ESRL/PSD using the R1 data/climatology, global relative AAM is nearly as low as early December 2007. The magnitude is ~minus 2 AMUs. In addition to the frictional torque, a strong recent negative global Coriolis torque (~20 Hadleys) has also been bringing global AAM down. Hence the global AAM tendency (calculated and computed) is ~minus 20 Hadleys, mostly from the tropics. In fact, there is already a signal of poleward propagation of this zonal mean negative AAM tendency off the equator.

Other terms such as the earth (mass) AAM are strongly positive (~1.5 AMUs) due to anomalous high surface pressure across primarily the tropical and northern subtropical regions of the globe. Finally, consistent with the GWO probable to orbit to phase 3 (more said below), while still complicated, a zonal mean AAM sink is again present across the Northern Hemisphere subtropical atmosphere with a source in the extratropics. This means (loosely) the eddies are again starting to flux AAM from out of the tropics into the extratropics, with the maximum transport ~30-35N. There is a weaker zonal mean signal of this flux divergence of AAM transport process across the Southern Hemisphere.

Given the low AAM base state and negative global tendency, the GWO has orbited to phase 2. This projection is well above 1 standard deviation, the strongest since December 2007 in terms of this quadrant of phase space. Hence we are observing more zonally oriented RWDs consistent with the GWO composites produced by Weickmann (paper in preparation by WB).

I do think there will be a circuit to phase 3 (legacy GSDM Stage 1) and beyond. Furthermore, having my reasons, I am going to be bold and offer that MJO #4 is probable. Knowing that timing is white noise, my thought is to be concerned about our El-Viejo base state being strongly amplified by early-mid March. Not only will this enhance an active March climatology, another episode of MJO variability “pissing off” La-Nina could be bad news for the USA and global locations already hit hard by severe weather (all types) since at least December 2007.

Issues discussed about the stratosphere last week still remain. Please see the following link for details.

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

Summarizing, I think there is an evolution involving the tropical convective forcing and global atmospheric circulation response which may lead to an enhancement of our La-Nina base state during the next few weeks. That includes the possibility of MJO #4 developing in the region of the Indian Ocean and the GWO orbiting to phase 3 and beyond. In earlier posts, given all the zonal symmetry concerns, I did not think constructive and destructive interference of La-Nina would still be an important issue. Obviously I have reconsidered that, and we will see what happens.

Probable weather impacts for the USA ~weeks 2-4 with more western states troughs should be easily apparent by now. This may literally be “the season of the witch!” As mentioned last week, higher latitude blocking may shift the central USA southwest flow storm track a bit south at times. Locations such as the Upper Mississippi Valley hit hard by severe winter weather may not only experience more of it, but also have “spring” delayed. Since it does not look like La-Nina is going anywhere any time soon, the track of what may be violent outbreaks of severe local storms is probable to shift northwest into the northern and central Plains/Upper Mississippi Valley heading into May and June.

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 will leave it to the expertise of the appropriate weather centers internationally to alert the public of these risks.

It is less clear to identify the regions where tropical cyclone formation is most probable. I think locations along the westward shifted SPCZ into the South Pacific Ocean islands need to be concerned about that hazard mainly week-1. Since there already are surface westerly wind anomalies across the South Indian Ocean, the tropical cyclone hazard is probable to increase there week-1. That may continue weeks 2-3 impacting locations from Madagascar to the north coast of Australia. Strong-severe frontal thunderstorm activity is probable to continue cross portions of tropical South America especially Brasil week-1 spreading into South Africa by week-2

Appendix

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

http://www.cdc.noaa.gov/map/clim/gsdm.shtml

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:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

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 1-2 March.

Ed Berry

Shoe Horns and Recipes will not Work on this Witch

Edited 18 February to clarify some points.

The spatial pattern of tropical SSTs from Indonesia into the Pacific Ocean is still consistent with a mature strong La-Nina, with negative anomaly magnitudes ~2-3C (totals ~24-25C) from the equatorial date line to about 110W. Slight positive anomalies have been appearing along the coast of South America for the past several weeks. One can speculate various reasons on the latter. However, with the seasonal cycle favoring warming, the cold equatorial anomalies cited above are not trivial.

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 South China Sea has led to substantial SST cooling across those regions. SST anomalies are ~minus 1-2C across much of the Indian Ocean to near Australia, having totals ~27-28C. The only positive (but weaker) anomalies of ~1-2C are from northeast of Australia into generally east of Philippines with totals ~28-29.5C. The spatial horseshoe pattern of positive SST anomalies extending into extratropical Pacific Ocean of both hemispheres continues to be very well defined, typical of a mature La-Nina (and emerging negative PDO signal, for folks who study that?).

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.

http://www.wmo.ch/pages/prog/wcp/wcasp/enso_update_latest.html

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 USA, and will continue for at least the next few weeks (more said below).

Full disk satellite imagery and other tools show the strongest moist tropical convective forcing centered ~10S/130E while still extending from eastern Indonesia and the Philippines southeastward into the SPCZ. The SPCZ has been shifted west, typical of La-Nina, and has impacted portions of Australia with severe thunderstorms and flooding rainfall per WMO. This region of enhanced rainfall strongly projects onto a MJO utilizing the WH (2004) methodology (#3 for the 2007-08 boreal cold season; ~1.5 sigma, with the ENSO signal removed), currently in phase 7 through 15 February. Most models (ex., the NCEP GFS) have been underestimating both the strength our current MJO and its rate of eastward propagation for at least the past 2 weeks.

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 Australia into the southwest Pacific Ocean eastward propagation is present. For example, surface westerly winds anomalies ~15m/s from the South Indian Ocean into the SPCZ has been present for at least the past 7-10 days. The latter have provided a source of background cyclonic relative vorticity for the development of several tropical cyclones including category-4 Ivan that is about to impact Madagascar.

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.

A Western Hemisphere dynamical signal is also steadily emerging, with eastward moving anomalous twin upper tropospheric subtropical anticyclones loosely straddling the date line (discussed below) and divergence increasing aloft over South America forced by the downstream cyclones. A valid suggestion (per WK(1999) coherent modes Hovmollers) is that the latter is a response from a convectively coupled Kelvin wave. However, the wind animations suggest MJO circulation anomalies are responsible for the increasing upper tropospheric divergence across tropical South America (as part of the Western Hemisphere decoupling process). Full disk satellite imagery has shown an increase in convection across that region during the last few days.

This MJO already has significantly impacted and is probable to continue impacting the USA for at least the next couple of weeks. One cannot simply look for wave-1 signals in the upper tropospheric velocity potential field to assess the strength of a MJO. There is no cookbook to understanding the dynamics of MJO variability particularly in terms of the non-linear forcing-response-feedback atmospheric processes currently going on.

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 South Pacific Ocean tropical convective forcing from MJO #2. RWDs, interacting with MJO #3 currently heading into the Western Hemisphere, have continued to force at times intense anticyclonic circulation wind flow anomalies across the Northern Hemisphere polar latitudes. That includes the western Canada ridge discussed above.

RWDs arcing from the western Canada anticyclone through the North Atlantic Ocean into Asia have forced another spike in the East Asian mountain torque of ~plus 15 Hadleys. However, this time there is a strong global component that has involved MJO #3, a poleward directed zonal mean AAM transport signal ~35N especially earlier this month (roughly 4-8 Hadleys), and a compensating frictional torque currently ~minus 10 Hadleys. The recent frictional-mountain torque index cycle variation is why the PNA index (Pacific-North American teleconnection) has become weakly positive. The point is that these highly complex non-linear interactions involving multiple time-scale processes has led to the extension of the East Asian jet (EAJ) that will slam the USA west coast, which the numerical models finally start to catch onto about 5 days ago.

Reading the above brings back memories of the recent “storm on steroids” that severely impacted the California coast ~3-4 January 2008. However, the former occurred while the MJO and GWO were evolving through phases 3-5 while what is about to occur may be with phases 7-8 of the WH (2004) MJO plot. Furthermore, the GWO may already be collapsing into phases 1-3 given other processes tied to, for instance, a negative Coriolis torque of ~minus 10 Hadleys. Again, there are no cookbook rules of thumb!

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 South Africa. This is why it is probable for a reasonable dynamical MJO signal to propagate rapidly through the Western Hemisphere possibly returning to the Indian Ocean by week 3. In fact, WH (2004) phase space RMM predictions from European meteorological agencies support this notion as suggested by the GSDM reasoning given here. The zonal symmetry issues discussed above have made good GWO signals tough to come by lately; however, I think a circuit to phase 3 (old GSDM Stage 1) is probable during the next few weeks. Whether or not we get MJO #4 is unclear.

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 Arctic. I will leave it to the reader to speculate on the predictive details. Again, stratospheric issues are only another feedback and trying to shoe horn them into AO/NAO etc., does not go well with me. Please see the following link for details.

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

Summarizing, the MJO dynamical signal is moving into the Western Hemisphere. While impacts from severe tropical convective rainfall are likely to be across the Southern Hemisphere, global weather including the USA will be affected by the MJO variability during roughly the next 1-3 weeks. Additional complicated processes explained by the GWO will also contribute. In terms of the tropical forcing and global circulation behavior, I speculate by weeks 2-3 the GWO will be orbiting around or near phase 3.

Most, if not all models (ensembles), have now captured the notion of the USA west coast focusing on California getting slammed by a southward displaced enhanced North Pacific combined jet stream by the end of week 1. Ramifications for those folks may be “similar” to the “storm of steroids” of early January, keeping in mind the magnitude of that event.

Troughs then moving into the Rockies leading to an intense southwest flow storm track across the central USA are quite probable. Should blocking start to develop across locations such as from Alaska into the Arctic, the storm track across the Plains may be shifted a bit farther south. In any case, the risk of the types of high impact weather experienced across the lower 48 states a couple of weeks ago may again increase weeks 2-3, perhaps enhancing climatology going into March (winter storms including intense-severe thundersnow Northern Plains and Upper Mississippi Valley, severe local storm outbreaks across the Deep South-Ohio Valley, etc.). Hopefully locations such as southwest Kansas into west Texas will get some of this precipitation instead of dry intrusions and even “southwest winds and blowing dust”.

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 Australia. Intense tropical cyclone activity may focus along the SPCZ into the South Pacific Ocean islands weeks 2-3. Strong-severe frontal thunderstorm activity is probable across portions of tropical South America especially Brasil by week-2 and South Africa by week-3, if not sooner (timing is always white noise!). Enhanced moist tropical convection may return to the South Indian Ocean by week-3.

Appendix

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

http://www.cdc.noaa.gov/map/clim/gsdm.shtml

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:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

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.

Ed Berry

Season of the Witch

The spatial pattern of tropical SSTs from Indonesia into the Pacific Ocean remains consistent with a mature strong La-Nina. Anomaly magnitudes are ~2-3C with the warmest north of Australia starting to extend into the South Pacific Ocean, and the coldest east of the equatorial date line. SST totals vary from ~31C north of Australia to less than 24C across portions of the Nino 3.4 region (latter NDJ value 1.4C per CPC). At depth per latest 5-day averaged TAO buoy data the cold anomalies extend to ~150-200m with positive anomalies around the equatorial date line (steep thermocline). Magnitudes are ~1-3C. The date line warmth appears to have weakened slightly during the last week possibly responding to a trade wind surge.

Cold continental air plunging south into the Arabian Sea in addition to past intense rainfall events has lowered SSTs considerably (totals less than 28C) in that region of the Indian Ocean. Additionally, positive SST anomalies have been slowly appearing along the coast of South America during the last several weeks. I will not speculate on the latter. However, the seasonal cycle favors warming of the equatorial Pacific Ocean waters, and it will be interesting to monitor any such impacts onto La-Nina. 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).

Full disk satellite imagery and the usual other diagnostic monitoring tools indicate the strongest moist tropical convective forcing centered ~5-10S/130E (with Western Hemisphere suppression), significantly farther east than when I wrote a discussion a week ago. In general, the region of strong-severe tropical thunderstorm activity extends from the central equatorial Indian Ocean east-southeast across northern Australia into a westward shifted South Pacific Ocean Convergence Zone (SPCZ). The SPCZ is loosely a graveyard of fronts from the Southern Hemisphere. At least 3 tropical cyclones are currently spinning across the South Indian Ocean, including category-4 Hondo.

In short, the Eastern Hemisphere tropical convective forcing is propagating east even faster than what I would have thought one week ago. In fact, my trusty back of the envelope calculation gives a phase speed of this forcing of ~8m/s south of the equator since about 20 January. However, the clusters of thunderstorm activity have slowed considerably during the last several days north of Australia (warm SSTs), and convectively coupled Kelvin waves have also been involved with the eastward movement. The WH (2004) methodology updated through 8 February gives roughly a 2-standard deviation MJO projection in phase 5. There are also other tools (coherent modes Hovmollers, Hovmoller plots of velocity potential, etc.) telling the world that MJO#3 for the boreal cold season is in progress.

While some brief coupling between the SSTs and large-scale convection may be occurring as I type, I think this tropical forcing will propagate into the Southwest Pacific Ocean along the SPCZ during the next couple of weeks or thereabouts (timing is always noise!!!). There are numerous reasons I now think so, and these may involve dynamical feedback processes that “linear-cookbook-shoehorn “meteorological reasoning”” may not explain very well (and difficult for the numerical models to represent).

I can only briefly elaborate here. One reason is we have had a nice SSTA perturbation of ~0.5-1C leading MJO variability much of the Austral warm season. As discussed above, while cooling has occurred across the western equatorial Indian Ocean, warming is now spreading into the Southwest Pacific Ocean east of Australia. Another reason is there has been extremely complex Rossby wave energy dispersions (RWDs) tied to the convection particularly into the northern extratropics during the last 2-3 weeks. The latter may be “pushing the MJO east” as a feedback into the tropics (one possible mechanism for this is discussed below).

Animations of upper tropospheric daily mean vector wind anomalies show the expected responses as the tropical convective forcing moves east. There are strong twin tropical/subtropical anticyclones centered ~90E and downstream cyclones just east of the date line. Anomaly magnitudes are ~20-40m/s with these features at 150mb, especially for the Western Hemisphere Pacific Ocean equatorial westerlies. At the surface anomalous south equatorial Indian Ocean westerlies extending into the SPCZ and date line trades complete the first order baroclinic response.

As already mentioned above, RWDs have recently been quite robust into the northern extratropics. In particular (see the ESRL/PSD animations), there has been a source from the west Pacific Ocean first tied to moist convection/twin anticyclones with MJO #2 (~mid January) then the twin cyclones with MJO #3 (not linear!). Responses have included strong synoptic-event anticyclones first across the North Atlantic Ocean around Greenland and recently Scandinavia. These features have guided RWDs southeastward across Asia keeping mean sea level pressures anomalously high east of the north-south mountain massifs in that part of the world. The baroclinic processes with the RWDs have been responsible for the earlier severe winter weather across China and most recently the intense Arctic air outbreak plunging into the Northern Plains as I type. Positive East Asian mountain torques (~10-15 Hadleys per ESRL/PSD R1 data plots) occurring roughly every 10 days has also accompanied these RWDs, adding westerly wind flow anomalies to the East Asian jet.

Finally, for those who watch the stratosphere, there may be another minor warming in progress linked to the RWDs. There is another recent spike in 10mb temperatures and upward directed 100mb zonal mean E-P fluxes around 60N. Please see the following link for details.

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

Loosely, after 2 strong going into 3 MJOs and various other sources for large-scale wind anomalies the last few months, the global circulation currently exhibits strong zonally symmetric circulation wind anomalies. For example, there are strong anomalous ridges across the subtropical-midlatitude atmospheres. There are also meridionally symmetric zonal mean zonal wind anomalies about the equator with broadly extratropical westerlies, subtropical easterlies then equatorial westerlies. That is why global relative AAM is near climatology given there apparently exists an equilibrium between processes wanting to add and remove westerly wind flow from the atmosphere. This may also offer some explanation for the recent weak signal of the Global Wind Oscillation (GWO). The point is that just as the SSTs exhibit mature La-Nina conditions so does the circulation response in the presence of unusual MJO variability (for a strong cold event).

Now it is a matter of rigorous daily monitoring to understand where the global circulation goes from here, especially given the upcoming transition seasons for both hemispheres. The notion of La-Nina becoming amplified or otherwise may no longer be relevant. Global AAM tendency (through 7 February) has dipped to ~minus 20 Hadleys with a contribution coming from the global mountains. Hence the GWO has weakly orbited to phase 1. A decent zonal mean poleward AAM transport signal (roughly 5-10 Hadleys) at ~35N has developed since the start of this month. The gist is that I would expect the global mountain torque to become positive soon particularly if the tropical convective forcing shifts into the west central-South Pacific Ocean per above.

Summarizing, there are a lot of complicated forcing-response-feedback (and subsequent interactions) dynamical processes going on as I type, leading to what some may view as a “simple global circulation”. I do expect the tropical convective forcing to shift into the SPCZ during the next couple weeks, adding westerly wind flow anomalies to the atmosphere. Interactions with the global mountains and extratropics may lead to a large AAM tendency soon allowing the GWO to possibly strongly orbit to first phase 5 (GSDM Stage 2), then phases 6-8. Whether or not MJO #4 develops during March is unclear. However, I have my reasons to speculate that AAM tendency may become strongly negative in a few weeks forcing the GWO to phase 3 (GSDM Stage 1).

There is general agreement among the numerical model ensembles from various weather centers of a trough-ridge-trough pattern across the PNA sector week 1 into week 2, with the ridge ~140W. This forecast is not unreasonable per above, and it does have some support based on DJF composite analyses done by Weickmann of both the GWO and MJO (WB paper is in preparation). Uncertainty becomes HUGE afterwards, mainly for timing. Numerical models are probable to struggle during the next several weeks not only because of seasonal transition, but also due to the issues already discussed.

A week ago I was thinking a GWO phase 3 response for the USA by ~16-23 February. By the end of that period there may instead be a strong North Pacific Ocean jet slamming the west coast linked to GWO phases 7-8. By weeks 3-4 (~23 February-8 March) phases 1-3 of both the GWO and MJO may be probable, leading to USA west coast cold troughs (extending from Alaska) and a southwest flow storm track across the Plains.

With the possibilities discussed in past postings, the ramifications of at times a severe winter weather regime for the USA unfortunately unfolded for much of the lower 48 states this past week. I do think there will “less intense weather” overall next week, keeping in mind model predictions of more closed lows developing across the Southern Plains. Any high impact weather should be focused east of the Rockies during the next 1-2 weeks, possibly including Arctic air. Attention may then turn to the USA west coast and Desert Southwest afterwards.

Per above, the risk of the types of high impact weather experienced across the lower 48 states this past week may again increase weeks 3-4 in similar locations (winter storms including intense-severe thundersnow Northern Plains and Upper Mississippi Valley, severe local storm outbreaks across the Deep South-Ohio Valley, etc.). I continue to have concerns about the developing dryness across the Southern High Plains from western Kansas into the Texas Big Bend. Enhanced subtropical jet activity at times extending into the Desert Southwest and Southern Plains may mitigate drought in these areas during this upcoming Spring.

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 appropriate weather centers to alert the public of these risks.

Tropical cyclone activity is probable to diminish across the South Indian Ocean while increasing north of Australia week-1. During week-1 and particularly ~weeks 2-3 severe tropical cyclones may impact the coasts of Australia given the warm SSTs. That risk should shift into the region of the South Pacific Islands afterwards. While suppressed week-1, strong-severe frontal thunderstorm activity may impact portions of tropical South America especially Brasil by week- 3.

Appendix

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

http://www.cdc.noaa.gov/map/clim/gsdm.shtml

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.

Links to CPC and PSD ENSO discussions:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

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 16-17 February.

Ed Berry

More Wraths From the Child of Darkness???

Indian-Pacific Ocean tropical SSTs (roles of global extratropical and Atlantic Ocean basin SSTs understood) continue to present a spatial pattern consistent with a mature strong La-Nina. Warmth remains across the Indian Ocean and particularly north of Australia while waters from the equatorial west Pacific Ocean to South America is generally still exceptionally cold. Anomaly magnitudes vary from plus 2-3C (totals ~30-31C) north of Australia to minus 3-4C from about 180-150W along the equator (totals ~24-25C).

Per 5-day averaged TAO buoy data the equatorial cold anomalies extend to about 150m depth with ~200m deep positive anomalies farther west centered on the date line. Magnitudes for the latter are around plus 6C and may be the early stages of an oceanic Kelvin wave. However, these deep positive anomalies were generated by a weakening of easterly wind flow anomalies on the equator forced by the previous MJO. The trades strengthening in that region once again may minimize any impacts from an oceanic Kelvin wave. However, that is speculation, and stay tuned. In any case, the very steep equatorial Pacific oceanic thermocline is also typical of a mature cold event.

Full disk satellite imagery and other diagnostic monitoring tools present a strong signal of tropical convective forcing centered ~5S/100E. This region of strong to severe thunderstorm activity loosely extends from South Africa to central Indonesia in a band roughly 10-20 degrees wide. Suppression is returning to the date line while the South Pacific remains sporadic, including Tropical Cyclone Gene.

The Eastern Hemisphere tropical convection does project onto a ~1 standard deviation MJO per WH(2004) methodology updated through 1 February. Whatever the case may be for the latter, I do think that projection will become more robust as the winds continue to respond to the tropical forcing (discussed below). My back of the envelope computation has components of this Indian Ocean forcing moving east from ~5-10m/s since about 20 January. I think this region is still getting its act together, and remember that it is important to understand the dynamics of the forcing and not shoe-horn it into a “name”. My feeling is the intense convection may soon stall north of Australia in the area of 120-140E given bath water SSTs there. As I discussed a week ago, the tropical convective forcing with what appears to be MJO #3 for the boreal cold season will likely amplify El-Viejo.

Animations of upper tropospheric daily mean vector wind animations show the expected response as tropical convective forcing intensifies across the Eastern Hemisphere. Strong twin tropical/subtropical anticyclones are developing across the Indian Ocean with down stream cyclones in the region of the date line. Anomaly magnitudes are ~20-40m/s with these features at 150mb, while at the surface equatorial Indian Ocean westerlies and anomalous date line trades complete the first order baroclinic response. Zonal mean easterly wind flow anomalies are returning to the tropical atmosphere while past subtropical westerly wind flow anomalies undergo dissipation involving “non-cookbook” dynamical processes.

There have been two recent interesting Rossby wave energy dispersion (RWD) events into the extratropics tied to the tail end of strong MJO #2 and the return of tropical forcing to the Eastern Hemisphere. I will only briefly discuss them here. Around 18-24 January a RWD occurred from the west central Pacific Ocean where tropical convection was still intense (GWO was orbiting into phase 5). A response was an anomalous anticyclone in the region of Alaska and northwest Canada. Courtesy of the Tokyo Climate Center (link below), zonal mean upward 100mb E-P fluxes ~60N became quite robust and 10mb temperatures rose ~60C in a few days toward the end of the month.

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

Temperatures have since dropped back to below normal and this event appears to have been a minor Sudden Stratospheric Warming (SSW). Tropospheric impacts are unlikely.

During this past week, while westerly wind flow anomalies were propagating poleward out of the subtropics, interactions of the synoptic eddies with the subtropical jet across the USA Desert Southwest led to a strong anticyclone in the region of Greenland. Whether or not this event initiates the road to a slightly negative phase of the NAO is unclear (models generally unsupportive). One important point (and there are others that can be made) is the latter is completely independent of the minor SSW discussed above.

As was expected, per ESRL/PSD AAM plots updated through 31 January, global relative angular momentum (AAM) is decreasing rapidly, ~minus 20 Hadleys computed tendency. The will decrease the length of day by ~5 milliseconds during the next few weeks, and I hope this is not a bad sign for the financial markets next week! Contributions are coming from the global mountain torque, particularly the tropics (East Asia should soon become negative), local frictional dissipation by the midlatitude eddies of those poleward propagating subtropical westerly wind flow anomalies, and a zonal mean sink developing ~20N. Global relative AAM itself peaked too slightly above the R1 data climatology during the last week of January. That was roughly 50-60 days after the last peak around 1 December 2007, which is consistent with both the GWO and MJO (loosely equals the GSDM) recurrence time scales.

Although still somewhat unclear, I think a strong zonal mean poleward AAM transport signal is developing ~30N (NE-SW tilts of the synoptic eddies support this notion). A response appears to be southward propagation of zonal mean westerly wind flow anomalies from the higher latitudes. Combined with anomalous zonal mean easterly wind flow anomalies ~35N (see past postings for thoughts about their evolution), once again ridges are well pronounced across the Northern Hemisphere midlatitudes (lesser Southern Hemisphere). Where these ridges set up regionally has a lot to do with who has feast or famine in terms of precipitation.

Updated through 31 January the GWO has orbited into phase 1 (GSDM Stage 4), and I expect that it will soon be at phase 3 (GSDM Stage 1). While the time scale is always difficult to estimate, I speculate phase 3 should be the case by the end of week-2, roughly in phase with both the MJO and La-Nina. The last occurrence of this kind of superimposition was around the first week in January 2008, when the “storm on steroids" slammed the USA west coast on about the 3rd.

Summarizing, it is probable that MJO #3 will amplify La-Nina during the next few weeks. While the repeatability has been remarkable this boreal 2007-08 cold season, seasonal transition soon into spring alone will add uncertainty to any subseasonal outlooks. Also adding uncertainty is if this current MJO will have periods of moving and stalling like the previous event. Finally, timing is playing with white noise!

Zonal mean westerly wind flow anomalies propagating southward (per above) suggest the continuation of progressive synoptic features across the USA for at least the next 7-10 days, with limited Arctic air. Recent model runs from various global operational weather centers support this reasoning, as would be expected.

However, there are large differences in the week-2 ensemble means of, for example, 500mb height anomalies. Some of these differences can be attributed to systematic biases and not predicting well the on-going evolution of the tropical convection in terms of forcing-response-feedbacks, etc. Based on DJF composite analyses done by Weickmann of both the GWO and MJO (WB paper is in preparation), I think it is probable to see more strong cold troughs hit the west coast later week-2 leading to a southwest flow storm track across the Plains roughly week-3 (~16-23 February). Arctic airmasses are likely to get involved, and risks of the high-impact weather detailed in past postings will again increase.

Finally, I have to express some concern about developing dryness across the High Plains from Kansas and Colorado on south. The current progressive regime is bad news for that region in terms of precipitation. This is a La-Nina signal, and a strong event like that going on suggests worsening drought. However, given the MJO and other variability observed the past several months, and that I am not a “recipe-cookbook” meteorologist, there is certainly reason to speculate improvement particularly going into spring. I hope that is not “wishing” on my part. If this dryness persists and worsens, southwest winds with blinding blowing dust and high fire danger conditions may occur relatively soon (Hell on earth?).

Per WMO and other information, there has been quite a bit of severe weather internationally during the last several weeks. Included are record cold and snow for portions of this Middle East and China, and severe flooding thunderstorms for portions of South Africa and Indonesia. While attributable (and not surprising) to the circulation behaviors discussed during past postings, I generally leave it to the appropriate weather centers to alert the public of these risks.

Locations from South Africa into much of Indonesia will likely continue to deal with severe thunderstorms and flooding week-1 then focusing on the Maritime Continent to the north coast of Australia weeks 2-3. The risk of intense tropical cyclones should shift to around Australia by roughly week-3. The Southwest Pacific Ocean remains our wild card, and Tropical Cyclone Gene should hang around for at least a few more days.

Appendix

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

http://www.cdc.noaa.gov/map/clim/gsdm.shtml

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.

Links to CPC and PSD ENSO discussions:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

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 9-10 February.

Ed Berry