Saturday, December 15, 2007

AAM Trend Still in Sync with the Financial Markets

I wish the upward trend in the USA financial markets a week ago would have continued this last work week. This makes me wonder if any statistically significant correlations exist between subseasonal-interannual atmospheric variability and the world markets. The former would be in regard to the GWO and MJO while the latter would relate to ENSO.

This posting only updates what I have been writing during the last few weeks. The spatial pattern of tropical SSTs across the Indo-Pacific sector is consistent with a mature La-Nina. Anomalies along the equator from 160E-South America remain negative with magnitudes at least minus 2.5C starting at 140W (per TAO buoy data). At depth these negative anomalies are at least 150-200m deep while comparable positive anomalies (~3C) remain in the region of the equatorial date line. The latter is a response to a deepening of the oceanic thermocline forced by a Kelvin wave initiated by the recent past MJO.

While the equatorial Indian Ocean has cooled during the last week from increased tropical convective rainfall, very warm SSTs are present from about the north coast of Australia to Indonesia into the South Pacific Ocean. SST anomalies are ~plus 1-2C from around 120E-180 south of the equator with totals generally in excess of 30C (86F). These very warm Eastern Hemisphere tropical SSTs will have an important contribution to the evolution of the global circulation during the next several weeks.

Per full disk satellite imagery tropical convective forcing has become very intense across the Indian Ocean centered ~5S/80-90E having OLRA less than minus 70W/m**2 per 3-day averaged BMRC plots. Compensating strong suppression exists downstream from Indonesia-date line. This forcing is tied to the MJO, with latest WH2004 plots projecting onto phase 3 due to RMM2 being strongly negative. For the time being, the MJO signal has stalled. The GWO (which also captures the circulation responses due to the MJO in addition to extratropical non-oscillatory forcing) has remained in-sync with the tropical convective forcing returning to the Indian Ocean. Phase 3 (old GSDM Stage 1) best describes the projection of the current global circulation onto the GWO. Anomalous trades from Indonesia-date line downstream from the convection are reinvigorating La-Nina.

About a week ago global relative AAM tendency crashed to ~minus 50 Hadleys (3-day average/R1 data climatology). As of 13 December this tendency did spike to ~minus 5 Hadleys with a large component coming from a renewed positive global frictional torque. The latter was ~plus 10 Hadleys, seemingly exhibiting a recent periodicity of ~60 days (consistent with the GWO). Strengthening trades throughout the global subtropics have contributed. However, global relative AAM has again become quite low ~minus 2 standard deviations with the redevelopment of intense zonal mean easterly wind flow anomalies (~5m/s at 200mb) throughout the global equatorial and subtropical atmospheres. Also helping to remove westerly flow from the atmosphere are the large north-south mountains, with the global mountain torque ~minus 15 Hadleys having a large component from East Asia.

Animations of upper tropospheric daily mean vector wind anomalies show the expected circulation characteristics per above. Twin subtropical anticyclones are getting better defined ~90-120E with downstream cyclones in the region of the equatorial date line. Westerly wind flow anomalies (~10-20m/s) are developing across the Western Hemisphere particularly across the Pacific Ocean. In fact, some of this upper tropospheric westerly wind flow is being directed toward the southwestern USA.

Zonally oriented rapid Rossby wave energy dispersions (RWDs) directed toward the USA emanating from the Indian Ocean tropical forcing have been a dynamical component to the recent stormy winter weather pattern across the country. Per EMC/NCEP web site visual verification of predicted NCEP/GFS week-2 ensemble means of 500mb height anomalies valid roughly the last 7 days verses observed did not capture the RWDs leading to the recent negative height anomalies across the Desert Southwest. The latter is not only a systematic bias issue, but also the inability of global models to accurately predict tropical convective forcing after about day 5. I speculate that numerical model performance at lead times greater than ~3 days may remain "unusually problematic" for roughly the next 1-3 weeks.

I suspect the GWO may exhibit one or two small roughly 5-10 day circuits around phase 3 (consistent with El-Viejo) before resuming its large orbit toward phase 5 (GSDM Stage 2) and beyond. The WH2004 MJO phase space plot will likely do the same before showing an eastward propagation signal once again. One reason I feel this way is that I think the Indian Ocean tropical convective forcing is likely to shift east-southeast toward the very warm SSTs north of Australia during the next few weeks.

Of course, as always there are large uncertainties about timing and synoptic details. However, I think it is probable for both the GWO and MJO to be in roughly phase 5 by early January 2008, as I discussed a week ago. The seasonal cycle will also have “its say in this matter”, since climatologically SSTs 29C and greater become covered with tropical convection during the first part of January. So, are we going to have a period of ocean-atmosphere coupling ~120E-180 south of the equator in about 3 weeks (with the onset of the Australian monsoon)? Are we going to see another decent GWO/MJO circuit afterwards? The answers to these types of predictability questions are unclear; however, I speculate yes.

A generally active weather regime is probable to continue for most of the country through at least the end of 2007. As I typed a week ago, the period from around Christmas-early January 2008 may be exceptionally stormy focusing on the Rockies and Plains in the presence of an Arctic cold air source. However, both coasts and Alaska are probable to have impacts from our active regime. I also think it is probable to see strong ridge amplification (greater than climatology) from just west of North America-Alaska by mid January per above reasoning. The latter would suggest an anomalous cold regime from east of the Rockies-east coast with the possible exception of the Deep South.

Internationally, the main tropical cyclone hazard should shift from the South Indian Ocean (Bay of Bengal understood) toward the region of Australia and eventually southwest Pacific Ocean weeks 2-3. Surface westerly wind anomalies ~10-15m/s in that region certainly support this notion. By that time the Australian monsoon should be on-going. Indonesia and even the Philippines are also probable to have possibly severe rainfall events by weeks 2-3. I would think the current Scandinavian blocking pattern should break down by week 3, possibly retrograding into the North Atlantic Ocean. In any case, cool/wet conditions seem probable for much of the Mediterranean region through week-2. Arctic air will continue to build up and expand across particularly Siberia as well as Alaska and much of Canada during the next few weeks. Finally, I hope the spirit of Gabrielle will rest for the warm North Atlantic basin until boreal summer 2008.


An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (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 the WH2004 “convention”.

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. I may not be able to post another discussion for at least a couple weeks; stay tuned.

Ed Berry


Jim H1 said...

Hi Ed,

Are you giving up on the idea of a deep western trough?

Thank you!

Ed Berry said...

Hi Jim,

Thank you for the comment. At least through the end of 2007, and perhaps very early January 2008, no. I think much of the western USA into the Plains on east will see "storm after storm". These systems are likely to reach max amplitude across the western states. What evolves during January 2008 may depend on our MJO still getting organized ~90E and whether or not coupling occurs with the very warm SSTs north of Australia. The latter would suggest the scenario I discussed in my post. However, if the situation we observed around 1 December were to be more persistent during much of January, that could be nasty for especially the central USA. Lots of uncertainty; stay tuned.

Ed Berry

Ed Berry said...

Hello again, Jim,

I am sorry I did not respond to your earlier question about earth AAM. We are referring to the earth-atmosphere angular momentum (total AAM) budget. Relative AAM is the atmospheric component. The earth component comes from the distribution of atmospheric pressure impinging on the surface, tied to the mass of air.

If the mass is less than normal, then that suggests low surface pressure and a negative earth component to the total AAM budget (and vice-versa). We look at the zonal mean mass anomalies in addition to the global quantity on the ESRL/PSD plots that you look at.

Ed Berry