Friday, February 27, 2009

La-Nina Impacts HIGHLY Probable to Continue at Least well into Boreal Spring 2009

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. Negative SST anomalies across all Nino regions have warmed ~1C during the last few weeks. There has also been some warming at depth along the equatorial ocean thermocline from ~140E to the west coast of South America (per TAO buoy data). However, similar to a year ago, a contribution to the warming may be the annual cycle. Recall during late boreal fall 2008 the Nino SSTs responded to the global circulation that was already exhibiting El-Viejo characteristics. Utilizing Nino 3.4 SSTs including the ONI as a measure of the ENSO situation was unrepresentative at that time, and that may be the case well into Northern Hemisphere spring. (note the initial projection) (link 18)

The global ocean-land-atmosphere dynamical system is well entrenched in a quasi-stationary La-Nina base state. In fact, and possibly linked to recent tropospheric impacts from the January 2009 major sudden stratospheric warming (SSW), global relative AAM is at the lowest value so far. Updated through 25 February, global relative AAM was ~minus 2.5 standard deviations below the R1 data climatology, similar to a year ago during the strong La-Nina. Put another way, just like the stock market has found a new “bottom”, so has AAM. Conditions in the stratosphere have returned to about normal.

The WB (2009) measure of the GWO during the last 40 days has ~2 sigma displacement toward octants 2-3 of phase space, essentially the La-Nina attractor. Not wanting to get too involved with the details of the current earth-atmosphere AAM budget (see plots), I think there may be another equilibrium "of sorts" of physical processes going on. For instance, the global frictional torque has recently spiked to ~plus 20 Hadleys, with most of that coming from enhanced trades. A portion of the latter may be coming from zonal mean negative AAM anomalies being brought down to the surface via mass circulations (enhancement of the Hadley cell; see earth AAM). In any case, this is an example of the atmosphere trying to get out of La-Nina, analogous to recent stimulus packages attempting to halt economic recession. There has also been an abrupt poleward shift of zonal mean AAM transport from ~35N to 50N, with a weak subtropical source. The latter is not good news for Northern Hemispheric locations experiencing drought.

Observationally, there have been several rapid variations involving zonally oriented Rossby wave energy dispersions (RWDs)/dispersive baroclinic wave packets during the past several weeks. In addition to causing difficulties with global numerical model predictions, these RWDs have also disrupted some of the tropical convective forcing. However, per full disk satellite imagery, enhanced rainfall is consolidating near 0/120-140E, while both tropical South America and Africa remain active. Retaining the interannual signal, through 26 February there is ~2 sigma MJO projection in octant 4 of WH (2004) phase space. However, in reality, there is no physically significant MJO variation of tropical convective forcing currently going on (past rogue MJO understood!).

Interhemispheric meridional symmetry of zonal mean zonal wind anomalies is well pronounced, including easterlies across the subtropical atmospheres. For the first time in at least a few weeks, the upper tropospheric zonal asymmetric portion of tropical circulation anomalies has returned. There are well defined twin cyclones near the Dateline (~30-40m/s anomalies at 150mb) with weaker anticyclones across the Indian Ocean. Anomalous midlatitude ridges continue to dominate the extratropics.

A loose superposition of phases 2-4 of both the GWO and MJO snr 250mb psi composite anomaly plots best depict the current global circulation. This type of circulation is probable to persist well into March, and possibly most of this upcoming spring. Because of on-going feedback processes not discussed, phase 5 of the MJO snr OLR composite anomaly plots may best represent the current tropical forcing, and, on average, may continue “until further notice”. The latter has generally been the case for the past 90 days.

Regardless of the details, little change in the overall synoptic pattern across the PNA sector is likely for at least the next several weeks. The La-Nina (and ENSO variations in general) characteristics of a global circulation “suddenly do not just go away (for reasons; insert angry Rottweiler!)”. There will be variations with the seasonal cycle, including shortening wavelengths that could lead to deep troughs across the central USA states (for example). More generally, on average, the outcome of temperature and precipitation anomalies for the lower 48 states during March-June 2009 may have some similarities to that same period during 2008. However, unlike 2008, subseasonal activity this boreal winter has been much weaker. While that could change, compared to a year ago, I am concerned that an outcome for boreal spring 2009 that is more consistent with the La-Nina composite signal may occur. This includes intensifying drought with anomalous warmth across the central and southern High Plains into Texas, possibly spreading northeast (see the U.S. Drought Monitor for other areas).

I trust the expertise of the appropriate meteorological agencies to alert the public of additional weather hazards worldwide. There have been some recent notable events, including extremely active weather from portions of the Mediterranean Sea into the Middle East. The latter may continue for at least another couple of weeks. Locations centered on Indonesia are likely to get hammered with intense-severe tropical thunderstorm activity for at least the next couple of 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 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 6-8 March 2009.

Ed Berry


Erl said...

"Utilizing Nino 3.4 including the ONI as a measure of the ENSO situation was unrepresentative at that time, and that may be the case well into Northern Hemisphere spring."

Agreed. Marked warming is occurring at 20-30°S

"In any case, this is an example of the atmosphere trying to get out of La-Nina, analogous to recent stimulus packages attempting to halt economic recession. "

Agreed, the tropics is warming and the Hadley is expanding. There is less cloud 20-30°S

Leif Svalgaard says this "there is a 22-year cycle in geomagnetic storms [and we know why] such that they are stronger from the maximum of even cycles to the maximum of odd cycles and weaker from the maximum of odd cycles to the maximum of even cycles. So the years ahead [until 2013] will see weaker storms [or rather the storms will have less effect],"

The Sudden Stratospheric Warming has proceeded in conjunction with a cooling of the equatorial stratosphere and a warming of the tropical ocean. That is historically a consistent relationship regardless of whether it occurs in the Arctic or the Antarctic.

The connection between the solar wind and tropospheric weather is via the solar wind effect on the density of the atmosphere above the pole vis a vis that above the equator. This changes the intensity of UV light that drives temperature in the interaction zone between the stratosphere and the troposphere where there is sufficient ozone to provoke a response. The high pressure cells that constitute the poleward arm of the Hadley cell are such a place. The solar wind blows, the upper atmosphere (ionosphere) is driven equator-wards by electromagnetic forces as the stronger magnetic field lines at lower latitudes produce greater uplift. The ions are vertically well spread some being present in the stratosphere during daylight hours. Its all pretty tenuous up there (troposphere has 75% of the total) and the neutrals are carried along with the particles with unbalanced electrical charges as they respond to electromagnetic forces. I think that that is what a cooling equatorial stratosphere in strict conjunction with a warming Arctic stratosphere tells us.

Its easy to see how we can get that strong warming at 20-30°S. Any increase in upper troposphere temperature will directly reduce ice cloud density, lower the vorticity in the subtropical high pressure cells, soften the surface atmospheric pressure in the east Pacific and weaken the trades. Eventually the warm water will find its way to the ENSO 3.4 region.

Ed Berry said...

Hi Erl,

Thank you for the interesting comments. I think there is a lot of uncertainty regarding the role of the solar cycle with SSWs, etc.. The January SSW may have been a completely random event, and our data sets are limited. We will see what happens.


Erl said...

Thanks Ed,
The thing that needs to be explained is the inverse relationship between temperature in the stratosphere in the Arctic and over the Equator. I don't think Rossby waves will do it.

The presence of erosive nitrogen compounds in the polar vortex varies with the aa index of geomagnetic activity. Stall the vortex and the Arctic lights up like a Christmas tree with ozone.
In an polar warming event we see a swift increase in ozone outside the area of the polar night prior to the onset of the event. To me that suggests that the vortex weakens before the event.

The relationship that gives the game away is that between 10hPa temperature at 65°N to 90°N and sea surface temperature 20N to 20S. When you look at the annual data its a very close relationship but for a brief period following 1963 and 1974 when Agung and Fuego forced sea surface cooling at the same time as the Arctic warmed.

Yes, it will be interesting to see just how much the tropical ocean warms. Every two years the upper stratosphere north of 60°N at 1hPa warms strongly as in 2003, 2005, 2007 and it seems 2009. But, the sun is still very weak, the aa index is at historically low levels and north of 60°N at 1hPa it currently looks like all the even numbered years. But, then again we are in a cooling trend and have been strongly so since 2006.

Some see random, some see patterns and sometimes its just plain confusing.

snoman said...

Hi Ed,

It looks like the long awaited 150W ridge is finally showing itself! We had it briefly a few days ago and is now expected to return by Wednesday of this week.

On another note...why are the ENSO SST's warming when the GLAAM, SOI, 200mb zonal winds, and tropical OLR all say we are in a strong La Nina right now? It almost seems the ocean wants an El Nino but the atmosphere reufses to let it happen! Do you think the extreme La Nina atmosphere will cause the SST's to begin to drop again?

Linda said...

I have been noticing SSTs in the Atlantic- Cape Verde-hurricane route- are much cooler than last year.

Are these conditions forecasted to continue?
Or are summer tropical Atlantic SST's difficult to predict?

(In other words, can current SSTs in the Atlantic effect the 2009 hurricane season)

Linda-in San Antonio

Ed Berry said...

Hi Erl,

Again, thank you for the comments. My point about the Rossby waves (RWDs, specifically) were the role they played initiating the January SSW. The latter was linked to a subseasonal event. The inverse relationship you discuss is climatology (for reasons). We will see how this La-Nina situation works out.


Ed Berry said...

Hi snoman,

I think the warming Nino SSTs are related to the annual cycle, similar to a year ago (climatologically warmest in ~March/April). It is unlikely these SSTs will cool, at least in the "near term". Let's see what happens going into 2009-10!


Brian said...

Ed, I think the positive feedback that is going on in the Western Plains is dramatic. Dry soil, continueing to get drier. Drier soil heating up more rapidly the next day promoting atmopsheric mixing and resulting in strong wind. Which in turn continues to dry out and bake the soil...etc. This type of feedback is, like you said, only going to intensify the drought in TX, OK, NM, CO, and western KS. Certainly not good news for the Winter Wheat crop... Thanks Ed, I enjoy your blog.

Brian Bledsoe
Colorado Springs, CO

Ed Berry said...

Hi Linda,

I think the cool SSTs you are referring to are a response to persistent cool northerly surface flow west of Europe. These northerlies show up in the recent 90-day mean, and are consistent with the synoptic responses seen across the North Atlantic most of the winter. See the following as an example of forecasts.

My speculation suggests the uncertainty will be higher than "normal" for predicting tropical Atlantic SSTs this upcoming boreal summer. We will see what happens as the extratropical influences ease.


Ed Berry said...

Hi Brian,

Thank you for the comments and positive feedback! For everyone's sake out here, let's hope that this drought situation will not be as bad as we "fear". Right now, I think there is good reason to be concerned about it.


Erl said...

Ed, Don't want to waste your time but I am very curious as to the "climatology (for reasons)", that explain the simultaneous cooling of the tropical stratosphere as the arctic stratosphere warms?

Ed Berry said...

Hello again Linda,

Quick follow-up to your question about the upcoming Atlantic hurricane season. Per my previous response, I think it is unclear what impact the current SSTs will have on this summer's Atlantic tropical cyclone activity. Those same SSTs could quickly warm going into summer, and we are not considering the subsurface (ex., like the TAO data for the Pacific). Presumably those with the data are.


Linda said...

Thanks Ed:

I looked at SST anomaly maps a few years back..going to the 2005 maps.
They showed Atlantic cooling this time of year too. So, I guess a lot can happen between now and September.

I enjoy your blog. I don't know anything about meterology. However, from what I'm able to understand it explains things.

I agree La Nina has put us in "recession". For us it has been a rainfall recession.

Linda in San Antonio

13 inches of rain 2008.
Avg rainfall 25-30 inches.

Ed Berry said...

Hi Erl,

The "climatology" I am referring to is partly the general relationship of tropopause slope to stratospheric temperatures. The higher tropical tropopause is colder than than that over the Arctic.

Processes that act on the tropopause (very loosely,broad brushingly speaking) may impact stratospheric temperatures. For example,upward wave energy propagation from the winter hemisphere troposphere into the stratosphere. Another example would be warming of the tropical troposphere (for "whatever" reason) which could cool the stratosphere above it while at the same time could lead to warming in the Arctic stratosphere.

Hope this is some help.

Greg said...

Wouldn't the east based QBO (I believe it's east based) also take part in how the Atlantic hurricane season plays out?

Ed Berry said...

Hi Greg,

Sorry for my slow response. People have tried to link the QBO with Atlantic tropical cyclone activity. My understanding is that the relationship is not clear, especially when subseasonal variations and ENSO are likely more important.