Friday, March 06, 2009

AAM Rally in a Bear Atmosphere

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.

Please see links below for global SST details. Little overall change has occurred during the past week. The anomalously cool SSTs recently observed across much of the North Tropical Atlantic Ocean and portions of the Caribbean may have had a significant contribution from extratropical processes. For instance, cold surges accompanying digging troughs into Europe have plunged well south into the tropics during much of the winter, as have similar surges off the USA east coast. The cold front that accompanied the eastern states snowstorm earlier this week is nearing the north coast of South America as I type. (note the initial projection) (link 18)

While displaced toward low AAM in phase space, a large, roughly 3 sigma variation of the WB (2009) measure of the global wind oscillation (GWO) has been occurring since roughly 12 February. This behavior has been the dominant component of the subseasonal weather-climate dynamical system within a well established La-Nina base state. The orbit has involved approximately octants 1-4, having a magnitude similar to those seen during boreal fall 2008. The dynamical processes explained by the GWO have been working to try to bring global westerly wind flow back to normal, somewhat analogous to Le Chatelier’s Principle for chemical equilibrium. However, I also think we are seeing an atmospheric variation analogous to a bear stock market rally, and, unfortunately, Le Chatelier’s principle cannot be applied to the latter.

More specifically, the current GWO orbit in phase space is relatively “clean’, following the chain of events outlined in WB (2009). This dynamical measure of the global circulation also provides some quantitative evidence that the extratropics have been recently forcing the tropics. Broadly, there was first strong poleward AAM transport during the first half of February centered ~35N, followed by a strong positive global frictional torque, then global mountain torque. Please see AAM plots for details. Presumably involving the eddies and mass circulations (on our list to quantify along with real-time diagnostics), downward transport of anomalous subtropical easterlies ramped up the frictional torque. Anomalous high surface pressures then increased the global mountain torque. Through 4 March, global relative AAM tendency is again becoming negative, forcing the GWO toward Octant 1 while orbiting around the La-Nina attractor.

Primarily zonally oriented Rossby wave energy dispersions (RWDs), observed during the past several weeks, linked to these complicated dynamical processes have subsequently impacted the deep tropics. For example, the upper tropospheric anomalous twin subtropical cyclones connected with La-Nina were forced west of the Dateline. Intense zonal mean easterly wind flow anomalies that have been dominating the subtropical atmospheres have also weakened a bit, while shifting poleward. In fact, there is even anomalous zonal mean westerly wind flow across the northern subtropics (~5m/s at 200mb), regionally in the Western Hemisphere.

All of these processes have been trying to “jump start” the atmosphere. Regional scale responses have included progression of the PNA central Pacific Ocean ridge-USA west coast trough pattern, and an amplifying central North Atlantic Ocean ridge (not the NAO; this is a dipole of anomalies). As expected given the GWO orbit, these synoptic evolutions can be seen fairly well from looking at phases 1-4 of the GWO 250mb snr PSI composite anomaly plots.

Consistent with our quasi-stationary La-Nina base state, tropical convective forcing remains loosely focused on Indonesia, centered ~0/120E. Per above, a “poor excuse” of a subtropical jet extends from the Northern Hemisphere twin subtropical cyclone near the Dateline into the USA Desert Southwest (with lots of mid/upper tropospheric cloud cover). At least diurnal convection continues across tropical South America and Africa. Retaining the interannual signal, the WH (2004) measure of the MJO has ~1.5-2 sigma projection in octants 4-5 of phase space. Subtracting out ENSO, the signal is much weaker. In this case, the latter is more realistic (need to understand how to interpret any index; the Rottweiler is always watching!), the MJO signal is negligible. Phases 4-5 of the MJO snr 250mb PSI composite anomaly plots best represent tropical circulation anomalies, as they generally have since boreal fall 2008.

Where does the atmosphere go from here? Unlike the current financial markets, relative AAM may have found a “bottom” for the boreal 2008-09 cold season. This behavior would be consistent with that seen a year ago. As I have already typed in past postings, La-Nina circulation anomalies are likely to linger well into spring (at least), with synoptic variations tied to GWO. Synoptic responses shown by the GWO snr 250mb PSI (and other variables) composite anomaly plots for ~phases 8-1 to 4-5 shifted toward low AAM are probable “until further notice”. These will work with the seasonal cycle. This suggests a preference of more progressive western and central states troughs. However, like the stock market volatility (and different from a year ago), there will be deviations including eastern USA troughs and transient ridges from Hell.

Numerical model performance has suffered significantly during the last several weeks literally due to the GWO. I think their forecasts for the next ~5 days are useable (predictability always decreases during transition seasons). During weeks 2-3, the added subtropical westerly wind flow (per above) may help to extend the East Asian jet (shifted north) into the western USA. That may contribute to more energetic progressive troughs including their expected possible high impact weather. This does include warm sector severe local storms (remembering tropical moisture transports issues through the Gulf of Mexico) and cold sector (thunder) snowstorms with individual baroclinic cyclones. However, drought conditions are probable to continue intensifying across the central and southern High Plains.

I trust the expertise of the appropriate meteorological agencies to alert the public of additional weather hazards worldwide. Notable events continue. Locations centered on Indonesia and working into the Philippines are likely to get hammered with intense-severe tropical thunderstorm activity for at least the next 2-4 weeks. An elevated risk of tropical cyclone activity is probable around the north coast of Australia the next 1-2 weeks.


All presentations from the 24 February 2009 GWO workshop are available via anonymous ftp. If you have not received information on how to retrieve these, let me know. There was excellent attendance at this day-long event, and feedback was strongly positive. We appreciate all the support!

Links to CPC and PSD ENSO discussions, and a new experimental forecast technique involving a coupled LIM (3rd link below):

The following are links to information about the stratosphere and other nice monitoring tools: (new stratosphere link!)

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)), is (still) awaiting publication in MWR. A pdf of an in press version can be downloaded from the following link:

In addition to the subseasonal snr composite anomaly plots, we would like near real-time discussions with “weather maps” to 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, and extremely unscientific!

I will attempt to post a discussion the weekend of 14-15 March 2009.

Ed Berry


JordanWeather Forecasters Team said...

Hi Ed,
How are you??
Thanks for your amazing post.

I want to comment on the point that talked about "Numerical Weather Prediction", the low accuracy very noticeable in our region, there are many mistakes even in the +24Hour range, and deadly mistakes!! As example the shape of the trough, temperatures at different levels, and others. I had a very hard work last week as a result of the low accuracy.

According to the weather prevailing now, after we had consecutive very wet systems since middle of February, we are now enjoying the sunshine, and the vernal temperatures. Today temperatures reached in Amman about 24c and tomorrow the forecasts indicates about 28c, and exactly the same day last week we had 7c as a max!! How is the atmosphere crazy!

Some signs start to show, that there is something serious heading for us sometime between 15-21 March, and there are signs for strong blocking over Western Greenland, also over UK and Western Europe??
Please advice what are your thoughts for the situation in our area?

Finally, we had huge amounts of rain in the last week system, and snow covered wide areas in the mountains. Some areas got their season average!!


Ed Berry said...

Hello Moh'd,

Good to hear from you! Glad that you are finally enjoying some nicer weather. I have been quite busy, like you.

I agree that the weather may get more active for you week-2, as ridging intensifies across the North Atlantic and possibly expands into the regions of Greenland and Scandinavia. In fact, there may be 2 centers that develop, one around northwest Europe/Scandinavia and the other possibly retrograding into eastern Canada/northwest Atlantic. We have seen "this kind of behavior" a few times already this winter.

We will see far southeast the downstream trough will develop. Worst case scenario is much of the Middle East could get hammered with another intense Mediterranean baroclinic cyclone having high winds and severe thunderstorms. I would think you active (wet) season should end soon.

Best regards,

Greg said...

Hello Ed,

From what I have gathered, the spike of SSTs in Nino regions 4 and 3.4 will soon stop.

Is there any chance of this becoming an official La-Nina ?

Also, from your last comment you made it appears that you believe there will be an anomalous strong -NAO, coupled with possible central/eastern U.S troughing according to your atmospheric update, it looks like there is potential for yet another major east coast storm.

I'm ready for spring, but I wouldn't mind another shot at a good snowstorm.

Thanks for your continuous dedication with the updates.

Ed Berry said...

Hi Greg,

Thank you for the comment and support! I did respond to your question on my previous post.

According to the criteria of 5 consecutive 3 month periods of minus 0.5C and lower for Nino 3.4, I would offer that is unlikely with our current cold event. However, CPC in their diagnostics discussion has been acknowledging we are in a La-Nina with the ONI less than minus 0.5C.

My feeling is ENSO is an interannual global variation involving the entire ocean-atmosphere-land dynamical system. From that perspective, one can argue La-Nina has been around since December 2006. At the very least, scientifically, a multivariate index for ENSO is much more representative. That is why I feel the the MEI is a much better measure than the ONI.

Finally, a period of a true -NAO may evolve ~week-2/3 which could increase the risk of another east coast storm. We will see what happens.


Greg said...

I did see your response on the previous post. From my understanding there is a sharp decrease in hurricane activity when we see an east phase QBO as opposed to a west.

"During the QBO, Atlantic tropical cyclones are more frequent when 30 mb winds are westerly and increasing, rather than easterly and increasing. There have been 44% more hurricanes and 74% more hurricane days during the west as opposed to east phase of the QBO."

I am not sure how the producer of this quotation came up with that statistic.

As much as I hate to see my 70 degree temperatures of today go by the wayside, one more winter storm to follow won't hurt.

JordanWeather Forecasters Team said...

Hi Ed,
Thanks for your reply.
In general, High Pressure developing over north Atlantic is not that good for my area, because low pressure systems dig into western and middle Mediterranean, and then goes NE far away from us, while some movement for the high pressure '' as you describe'' to the east could somehow help us for harsh winter to be back! Because there is a well-developed cold area over Eastern Europe in the next 2 weeks so any ridging could enter Europe most probably will force that cold air to stick towards the Middle East directly.

I want to ask you about the following map (, is this map we could describe as a similar pattern expected for the next 2 weeks?? Although the map I put is for January not March.

Thanks for your responds and rich information,

Ed Berry said...

Hi Greg,

Thank you for the feedback. I have also read/heard similar results relating QBO phase and tropical cyclone activity (ex., Bill Gray). The physical reasoning has generally been that the easterly (westerly) phase enhances (decreases) vertical wind shear in the upper portion of the storms.

I can see some rationale to this thinking. However, we have not yet incorporated the QBO into our GWO work. There have been numerous occasions I have given some speculation during a "weather-climate event".

Enjoy the warm weather!

Ed Berry said...

Hello Moh'd,

Thank you for the response. I think the January map you show would be an extreme case meaning Arctic air plunging well into the Mediterranean (Med). However, my thought would be more troughs digging into the Med then shifting your way. Any cold air (not Arctic) across eastern Europe will likely get dislodged by them.

During ~week-2 there may be enough ridge amplification west of Europe that would increase the odds for Arctic air (for this time of year) to get involved with these systems that could impact the Middle East. In any case, you know your region a lot better than I do.

Take care,

jam472 said...


Thanks for the blog. Us down in Southern California, and even in California are under a state emergency, due to the drought. We are concerned about the drought, and how La Nina, the past two winter seasons, has provided very little rain fall, and marginal snow pack in the sierra's. Therefore, Do you feel the current Pacific ridge that is retrograding back towards the west coast from 150W, will in fact move back to 160W, to allow some more pacific troughs to enter our state by the end of the month? Currently, the GFS and CPC indicate the next 10-14 days, as having much below precipitation, and much below temperatures for the west coast, which is not contusive for our situation. Any thoughts you can shed on the situation, would be appreciated.


JordanWeather Forecasters Team said...
This comment has been removed by the author.
JordanWeather Forecasters Team said...

Hi Ed,
Thanks for your response, and I will be monitoring and inform you.

GFS ensembles are shocking for the period between 21 and 23 March, I hope they are true!

Take Care,

Ed Berry said...

Hi Jason,

Sorry for my slow response. Retrogression is occurring as I type. It will be a matter of how far south the next trough digs while still in the east Pacific.

Yes, I would be much more confident for locations such as SFO on north receiving decent precipitation starting ~late week-2 through week-3. However, this base state favors anomalous ridges suggesting deeper troughs having AWB characteristics. Bottom line, there is some hope for southern CA; however, drought breakers are unlikely. The same can be said for the central and southern High Plains.