Saturday, December 13, 2008

Entering Week-3 of the “Extreme”

The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”

Please keep in mind the ESRL/PSD GSDM web link, below, while reading this discussion.

The 91-day signal to noise ratio (snr) anomaly composites are being updated daily. There are still some map room issues that will hopefully be resolved soon. WB (2009), part-1 of a 2 part paper where the GWO is formally introduced, is in press for MWR publication. There is a link in the Appendix to download the manuscript.

These discussions are part of an experimental effort involving linking weather and climate. We are moving forward on having a one-day workshop in Boulder during February 2009 on the WB (2009) GWO. Details will be forthcoming.

The warmest ocean waters globally extend from central Indonesia to the north coast of Australia then into the southwest Pacific Ocean. SST totals are in excess of 30C with anomalies ~plus 1-2C. Negative anomalies along the equator from ~160E extending into all Nino regions persist, having magnitudes varying from 0.5-2C and totals generally well under 28C. In fact, latest 5-day averaged TAO buoy data shows ~minus 1C anomaly near 0/140W with roughly minus 5C at 125m depth. Overall, there is little change in the spatial pattern of global SSTs. The PDO is strongly negative; the tropical Atlantic Ocean remains warm, as does the southwest Indian Ocean.

Responding to the global atmospheric circulation, basin-wide cool SST conditions have been observed for at least the past month across all Nino regions. A recent disruption of the trades across the west central Pacific Ocean may have excited a downwelling oceanic Kelvin wave; and impacts from it, if any, are unclear. (note the initial projection) (link 18)

The wind and convective signals have shown some evidence of getting into sync during the last few weeks, as have the tropics and extratropics. However, they are still not lined up (GWO octant 1 verses MJO octant 4 in phase space – discussed below), and the interactions are exceptionally complicated. The dynamics of these processes are too difficult to discuss (at the level we are comfortable with) in a medium such as a blog. Only a few highlights are given in the following, and relevant material presented in my last few postings will not be repeated.

As was anticipated from monitoring the dynamics explained by the WB (2009) measure of the GWO (loosely stated), moist intense tropical convective forcing has reasonably consolidated ~0/110E extending from the southern Arabian Sea east-southeast into northern Australia. There is some “sputtering” tied to frontal activity across the warm southwest Indian and Pacific Oceans, while tropical South America and South Africa are at least climatologically active.

Retaining the interannual and ENSO signals, there is ~1 sigma MJO projection in octant 4 of WH (2004) phase space. In fact, phase 4 of the WH (2004) MJO snr 250mb psi composite anomaly plots reasonably depicts the current global tropical circulation. However, in my view there is currently no real coherent MJO signal of tropical convective forcing. We are observing a quasi-stationary La-Nina like component of the global ocean-land-atmosphere system. Furthermore, any notions about an active MJO signal in the west central Pacific are simply incorrect. A few techniques and tools suggest the latter. This type of misinterpretation serves as an example of what results when care is not taken to understand the dynamics of fundamental atmospheric processes including monitoring constant everyday non-linear interactions (yes, the Rottweiler is barking)! An overview and simplified brief attribution of “what recently happened” is given in the following paragraph.

Animations of various daily mean vector total and anomalous wind fields for the last 1-2 weeks do suggest strong tropical-extratropical interactions especially across the Eastern Hemisphere. As a response to the tropical forcing, twin upper tropospheric anticyclones redeveloped across the Indian Ocean. Poleward directed Rossby wave energy dispersions (RWDs) from the anticyclones, interacting with midlatitude wavetrains, resulted in the formation of anomalous twin upper tropospheric west central Pacific Ocean cyclones. This evolution was a re-invigoration of the zonally asymmetric wave 0/1 of La-Nina tropical circulation anomalies observed since at least early October. There was subsequent equatorial moist convective development forced by the twin cyclones, and even a weak westerly wind episode, leading to the above mentioned trade wind interruption. Leaving Tropical Cyclone (TC) Dolphin in the wake, the west Pacific Ocean trades are resuming and convection is disorganized.

Through 11 December the WB (2009) measure of the GWO had ~1 sigma projection in octant 1 of phase space. However, this data point is along a recent trajectory having a magnitude of 3 sigma at times. Making use of this GWO variation along with the 250mb snr psi composite anomaly plots (phases 7-8-1), this was one very important consideration to anticipate several weeks ago (before the models and official forecasts) the on-going retrogression of PNA circulation anomalies leading to a western USA trough. Additionally, the excursion toward “high AAM” has been the largest this year, and part of a trend to increase global westerly wind flow since March. Identifying the latter was one of my reasons when I suggested several months ago that while boreal cold seasons 2007-08 and 2008-09 may have similar circulation characteristics, an important difference may be greater zonal mean subtropical westerly wind flow this winter. So far, this speculation has been correct.

Global relative AAM has dipped to slightly below the R1 data climatology while its tendency remains weakly negative. Recent significant anomalous zonal mean westerly wind flow in the subtropical atmospheres has largely been removed through frictional dissipation especially across the North Pacific Ocean. Poleward fluxing of AAM with maximum divergence ~40-45N has continued since late November, and zonal mean anomalous easterly wind flow is getting re-established ~30-40N (5-10m/s at 200mb). The latter are actually part of an equatorward shift. Finally, the global mountain torque is ~minus 20 Hadleys while the global frictional torque may soon become positive (see plots for zonal mean contributions). The point, these and other components of the earth-atmosphere angular momentum budget that contribute to the WB (2009) measure of the GWO suggest a “resurgence of La-Nina”. However, I think it is unlikely to see the 2-3 sigma global La-Nina situations like that observed boreal spring 2008.

Phase 1 of the GWO 250mb snr psi composite anomaly plot best represents the extratropics. I still do think coupling in ~GWO and MJO phase 3 (La-Nina) is a possibility during the next few weeks, with perhaps variations in ~phases 3-5 for several weeks going into 2009. Loosely that translates to central/eastern Pacific Ocean ridging with western and central USA troughs. Of course, shifting around of anomalies across the PNA sector will occur due to unpredictable “synoptic noise/interruptions” (i.e.; for example, western ridge/eastern trough from time to time). Weather ramifications (should be easily understood by now), including the elevated risk for high impact events, can be seen from the corresponding snr composite anomaly temperature and psi plots.

The role of the anomalously warm Australian and southwest Pacific Ocean SSTs for the USA and globally will clarify (seasonal cycle) during the next several weeks. Typically the 29C and greater SSTs become “covered” with intense moist tropical convection starting around early January. Whether or not there will be a resumption of coherent eastward shifts of tropical forcing projecting onto bona fide MJOs is unclear. Speculation suggests a rendition of our La-Nina like state will continue through at least JFM, but with situations having anomalous subtropical jets and possibly even episodes of strong East Asian/North Pacific Ocean jets slamming the USA west coast.

Internationally, the focus for intense to severe tropical thunderstorm activity is probable to continue across the Eastern Hemisphere centered ~100-120E the next few weeks (shifting slowly south). Locations to be impacted include much of Indonesia and northern Australia. At least climatologically intense diurnal thunderstorm activity is likely for tropical South America and South Africa. In fact, the “La-Nina side” of the GWO/MJO OLR snr composite anomaly plots suggests enhancement shifting toward southern and western Brasil with time, while suppression may occur across the “Nordeste”.

The tropical cyclone hazard for both the west central Pacific Ocean (both sides of the equator), and the Indian Ocean/Australian basins is unclear. However, the greatest risk may be in the region of the South Indian Ocean toward Madagascar week-1 then shifting into the region of the northwest coast of Australia week-2 (TC Dolphin understood). Please see the latest official tropical cyclone forecasts for all basins.

I trust the expertise of the appropriate meteorological centers to alert the public of additional weather hazards worldwide. For instance, anomalous cold Arctic air is finally building up in both Siberia (surface temperatures ~minus 70F) and western Canada. Arctic air from western Canada is plunging into the Northern Rockies as I type.


Links to CPC and PSD ENSO discussions:

The following is a link to information about the stratosphere and other nice monitoring tools:

The following is a link to NCEP model verifications (surf around for lots more) .

The following is a link discussing recent global weather and related events:

These are probabilistic statements. We hope that an opportunity will arise for us (soon) to allow our dedicated web page effort to mature, expediting objectively and accountability. This web page effort will hopefully include an objective predictive scheme for the GWO with hindcasts.

The WB (2007) paper on the GSDM has been published in the February issue of MWR. The first of a two-part paper, where WB formally introduce the GWO (WB (2009)), has been accepted for publication MWR. A pdf of the in press version can be downloaded from the
following link:

In addition to the subseasonal snr composite anomaly plots, we hope near real-time discussions with “weather maps” will become a routine part of the ESRL/PSD GSDM web site sometime soon. Part-2 of our GWO paper will discuss the latter. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships. An important purpose is to provide a dynamical weather-climate linkage framework to evaluate the numerical models in a sophisticated manner as part of a subseasonal (and any time scale) forecast process, in addition to a climate service for all users. Relying on the numerical models alone is a cookbook! I plan on posting a discussion the weekend of 19-21 December.

Ed Berry


roqs2stoned said...

Take a look at that big pool of sst warm anomalies off the southern portion of south America in the pacific thats been building for a few weeks and tell me how you think it will affect the ENSO in the next month or two, porfavore.

Ed Berry said...

Hi rogs2stoned,

Thank you for the question. The total SSTs are less than 22C and anomalies are a response to the extratropical circulation. Bottom line, I do not think there will be any impacts to ENSO variability at least for the next 1-2 months.