Friday, December 19, 2008

Sinking Deeper into La-Nina?

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 about mid-February 2009 on the WB (2009) GWO. Hopefully details will be available next week (22-26 December).

The warmest SSTs globally still extend from northwest of Australia to the Dateline ~10-15S, with totals in excess of 30C and departures from climatology greater than 1C. However, significant cooling of equatorial central and eastern Pacific Ocean SSTs has occurred during the last 1-2 weeks, with nearly minus 1C anomalies across all Nino regions per 5-day averaged TAO buoy data. In fact, SSTs are ~minus 1.5C below normal at 0/160W, and anomalies colder than minus 5C are present at 125m depth/135W. The subsurface equatorial Pacific Ocean anomalies are now very similar to a year ago (steeper than normal thermocline).

Bottom line, this is the type of “Nino SST” response that has been anticipated by us since at least early October, in the presence of the global ocean-land-atmosphere dynamical system exhibiting La-Nina characteristics (with variations) arguably since December 2006. How much additional Nino cooling occurs is unclear; however, “my expectations (in terms of magnitude)” have already been exceeded. (note the initial projection) (link 18)

The wind and convective signals are once again are out of sync for at least the third time since October. Perhaps this is a characteristic for a “second year La-Nina”. Tropical convective forcing is somewhat disorganized, with enhancement focused on central Indonesia into northern Australia, tropical South America and South Africa. The latter is attempting to expand into the southwest Indian Ocean, and there is a strong flare-up over the southern Arabian Sea.

Updated through 18 December, the WH (2004) measure of the MJO shows a ~1.5 sigma projection in octant 7 of phase space; i.e., the west Pacific Ocean. Retaining the interannual and ENSO signals gives literally no projection. The latter is much more reasonable. The "artificial" west Pacific MJO signal is coming from the winds. The dynamics responsible for those winds are more accurately explained and properly represented by the WB (2009) measure of the GWO. I will only summarize below. Please see the AAM and other plots for details.

Since about mid September, with the important exceptions of two large ~3 sigma 20 to 30-day variations of the WB (2009) measure of the GWO, ~10-day orbits tilted toward low AAM have occurred. More generally, if a 90-day averaged location in phase space of the GWO is calculated, there would be a drift towards octants 8-1-2. The November orbit was slower, with a large excursion toward high AAM, and had better interactions with the tropics. There was considerable frictional dissipation of anomalous subtropical westerly wind flow during the November variation linked to extratropical storm track activity especially across the North Pacific Ocean.

In any case, the two large variations loosely involved first poleward AAM fluxes, then positive surface torques and finally interhemispheric positively phased subtropical wavetrains (Branstator (2002); +SWT). These +SWTs have had phase speeds of ~20-25m/s, and aligned by the base state have maintained the upper tropospheric zonally asymmetric wave 0/1 La-Nina distribution of tropical circulation anomalies consisting of twin Indian Ocean (Dateline) anticyclones (cyclones) that has been present since early October.

A strong poleward AAM transport signal (all part of eddy feedback processes from our quasi-stationary La-Nina global circulation state) appeared ~1 December (maximum transport ~40N) leading to a similar chain of events as described above. However, the response of the global surface torques was apparently “damped” suggestive of the current on-going weaker and faster GWO orbit through phases 8-1 to 4-5 then 8-1 behavior. The accompanying +SWT, however, is quite robust with wind speed anomalies ~40-60m/s at 250mb. In fact, with strong poleward AAM flux once again, similar to 2007-08 an interhemispheric positive phase of a Branstator (2002) circumglobal teleconnection meaning anomalous midlatitude ridges is back.

So, sparing anymore “Gone with the Wind”, I think our quasi-stationary La-Nina base state is continuing to mature. While currently just slightly below the R1 data climatology (through 17 December) after the plus 2 sigma November excursion, how low global AAM may drop is unclear. There is nice meridional symmetry of zonal mean zonal wind anomalies featuring equatorial westerlies, strong subtropical easterlies (5-10m/s at 200mb both hemispheres) then westerlies across the higher latitudes. It is probable this La-Nina situation will continue at least well into boreal spring (yes, more and more coupled models have been catching on, and other “organizations” are starting to “yield” a bit).

Responding to increasing regional scale divergence forced by +SWT, tropical convection is probable to increase across the Indian Ocean during the next 1-2 weeks. The details are unclear. However, by early January there should be a large region of intense to severe thunderstorm activity from roughly the equatorial Indian Ocean into Western Australia possibly focused ~5S/90-100E. Perhaps at that time the wind and convective signals will get back in sync, and “stay that way”.

Evolutionary behaviors depicted by phases 8-1-2-3 of the GWO 250mb snr composite psi anomalies are likely to represent the extratropical circulation at least through week-2. USA weather ramifications including the likelihood of additional extreme weather events should be “common knowledge” by now. For reasons, there is a bit of a historical maximum for significant/severe winter storm development to occur on the Plains during early January. We will see if that is the case for January 2009.

Speculating farther into next month, uncertainty increases because of seasonal cycle issues. I am still concerned that at least episodic events of enhanced convection across both the warm southwest Pacific and Indian Ocean/Australian regions may occur simultaneously. The role of MJO activity is uncertain. Bottom line, lack of MJO (additional MJO) variability may suggest a circulation tilt toward that shown by the snr 250mb psi composite anomalies for GWO phases 8-1-2 (3-4-5). On average JFM may see anomalous cold/wet (warmth/dryness) shifted toward the USA west coast into the Northern Plains (Deep Southeast), a slight westward displacement from 2007-08. There would still be an active southwest flow storm track across the Plains, but perhaps locations such as the Dakotas would have an increase of “the classic Great Plains blizzards from days back”. Finally, given recent behaviors, drought conditions (there is a multiyear component) may return to portions of the High Plains especially from west Texas into southwest Kansas.

Internationally, the 3 regions of enhanced tropical rainfall discussed above are likely to continue through week-1, with consolidation probable across the Indian Ocean into Western Australia at least weeks 2-3. Frontal thunderstorm activity may become quite intense across portions of Australia going into January. Regardless of the behavioral details, most of Indonesia and even the Philippines (at times) are likely to experience anomalous rainfall including severe thunderstorms and flooding “until further notice”.

The focus for tropical cyclone development may shift into the South Indian Ocean (TC Billy and Cinda understood) to the northwest coast of Australia during austral summer. In fact, an increase in that region to above climatology is possible during weeks 2-3. I would be surprised not to see at least one or two tropical cyclone developments along the SPCZ east of Australia into the South Pacific Islands during JFM given the very warm ocean temperatures. 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. There has been an increase during the past week.


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 27-28 December.

Ed Berry


roqs2stoned said...

The next month or so will be fun to watch. The thermocline looks prime and ready, cold ssts moving in from the north... but that trump card is still the warm ssts moving north along S America. I'm not sure if the ssts in the Nino 1+2 or eastern portion of 3 will be cool enough to change the atmosphere above them and get the air there to decend. Plus it's late in the season for a significant ENSO event to occur. Using ONI as a ref, I'd say that the best we'll have after April 09 is a cool neutral event... very weak La Nina at best.


Ed Berry said...

Hi Mike,

Thank you for the comment. ENSO encore events are typically weaker than a previous strong situation. However, our sample size is limited meaning there is a lot for all of us to learn. How strong La-Nina may be boreal spring is unclear; however, the signal is probable to persist.

You are correct about the seasonal/annual cycle and other SST issues (that we are very well aware of). A significant portion of our work is to identify subseasonal variations that are departures from climatology.

Please remember that I am referring to a global weather-climate situation (ocean,land, atmosphere) about ENSO. In fact, I use the terminology "El-Nino", "La-Nina", etc., to communicate. Folks can relate to that much easier than saying, for example, "low AAM base state favoring poleward fluxes and AWB".

The ONI is incomplete, and many good scientists agree with that assessment. Coupled GCMs alone illustrate the weaknesses of ONI. For example, the warm Indian Ocean contributed to shutting down the basin wide (including Nino 3.4) El-Nino going into the 2006-07 boreal winter. A much more complete measure of ENSO, that is also the WMO standard, is Klaus Wolter's MEI.


roqs2stoned said...

Hi Ed,
Thanks for your response. Let me begin by saying I intend this to be a constructive discussion... so many people get the wrong idea when suggestions or disagreements are made.
When I mentioned ONI, I only meant it as a reference. When I think of ENSO, I tend to primarily consider the equatorial zone from 05 to -05 longitude, or the area not affected by the corolis effect, and from Peru to Indonesia. I think that this zone, because of the lack of corolis is somewhat a different zone than higher latitudes, and that consideration is too often left out when folks consider how ENSO works.
I went back and looked at both ONI and MEI and saw that ENSO encore events were not much more likely to be weaker or stronger than the initial event. In fact, it looked as if La Nina's lasted 1 or 3 years with an exception or two. That is probably because different ENSO events have different causes and are sustained in different ways. For instance, the La Nina event beginning in early 2007 was a reaction to the previous El Nino of late 06 and early 07. An El Nino did not occur after the La Nina subsided this year because cool anomalies coming from the north (and into 3.4) blocked the propagation of the warm tongue, if it were not for this sea surface behavior, the warm tongue would have propagated beyond the date line (the trades being weakened by the lack of temperature difference between the east and west Pacific) and the next Kelvin wave would have kicked off an El Nino.
Now that the 2007-2008 La Nina is over, we are headed into what appears to be another La Nina (or cool neutral). This La Nina will probably be sustained by those same cool anomalies arriving in 3.4 from near California (probably a function of PDO).
The real question in my opinion is; will the trades near the Galapagos gain enough strength to cause enough upwelling that will cool the surface enough to change the structure of the atmosphere above and cause it to descend in that area (which will in turn cause even stronger equatorial trade winds and further upwelling).

While I view ENSO as primarily a cause of different local effects, that should not be construed to mean that the macro-atmospheric circulation is not involved. However, I view it more as a minor cause.

Ed Berry said...

Hi Mike,

Again, thank you for taking the time to read these discussions and post comments. I think it goes without saying that all scientific exchanges are meant to be constructive. We are in an area of work where the unknowns far exceed what we hope is understood.

Much of what we deal with is red noise; that is, processes that grow and decay. As has been the case this fall, red noise signals such as the observed large GWO variations offered information to make opportunistic skillful forecasts. That included the return of La-Nina and associated weather impacts.

What is written below is only kindly offered to you for your consideration. I can only wish that at some point (and we are working on this) we will be able to present weather-climate information in a much more friendly platform than these blogs. That would facilitate significantly improved interaction.

The earth's rotation imparting what most understand as the "Coriolis force" onto the atmosphere is one of the fundamental principles of atmospheric dynamics (an apparent force). The latter is considered when deriving the equation of motion, which is also a statement of conservation of momentum. Hence the AAM and GWO plots.

The winds that circulate into the deep tropics (and affect the SSTs) including along the equator are very much impacted by the earth's rotation. In fact, there would not be large-scale persistent trade winds along the equator if it were not for the Coriolis force (ex., the large-scale climatological subtropical anticyclones).

ENSO variability is a global phenomena. While subseasonal dynamics and other components are definitely important, ENSO is not a residual.


roqs2stoned said...

Hi Ed,
Last April we also predicted the return of La Nina this year but our prediction was based on the cool ssts from the north and into the 3.4 blocking the eastward propagation of the warm tongue. As it turns out, observations supported this prediction.

Captain Climate said...

Hello Ed;

Late Merry Christmas.

Accurate New Year!!!

We are blessed to experience some of the most interesting weather in our lifetimes AND have greater ability to measure and observe than ever.


PS: Getting excited about the prospects of an East Coast Winter Storm Jan 2-4!

mystery ham said...

How Do You Like This Headline ?

"World Crops Threatened by Strengthening La Nina Weather Pattern "

Ed Berry said...

Hello Dean and "mystery ham",

Thank you for the comments, and Happy New Year!!! We will see what happens along the east coast 2-4 January, the possibility is there.

Many of us have been concerned about the real possibility of this La-Nina encore since at least late September 2008. How that information would have helped the world crop situation (and ramifications) is always an interesting question.

Ed Berry