Saturday, January 10, 2009

The Devil Deals the Atmosphere; PNA Retrogression or Bust!!!

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 map room issues that are being worked on. 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 a component of an experimental effort involving linking weather and climate. The formal announcement for the 24 February 2009 one-day (~9am-5pm MST) workshop on the WB (2009) GWO has been released through various mailing lists. If you have not received this, please leave a comment with your email address, and I will forward. Hopefully we can place this information on the above GSDM web link ASAP.

The general spatial pattern of global SSTs and their anomalies persist (see links). Tied to recent variations of atmospheric and tropical forcing (more said below), a slight lessening of the cool Nino anomalies has occurred during the past week (~minus 1-2C per 5-day averaged TAO buoy data). In fact, there is a downwelling oceanic Kelvin wave ~100-200m deep crossing the Dateline. The very warm waters of the Southwest Pacific Ocean have cooled substantially with totals generally less than 30C.

In any case, in terms of the global ocean-land-atmosphere dynamical system, La-Nina is well established. The expected re-emergence became notable by about October 2008, atypical timing based on our limited sample size. Consistent with “encores”, our on-going La-Nina is weaker (but more robust than earlier anticipated by myself) than a year ago (per GWO, MEI, SSTs, etc.). (note the initial projection) (link 18)

During the past 1-2 weeks the wind and convective signals did reasonably get back into sync. The result has been a perturbation destructively interfering with La-Nina. Behaviors similar to this were observed relatively frequently during the strong 2007-08 cold event. Unlike a year ago, however, the quasi-stationary component of the global circulation has been the most dominate.

In my last posting (3 January 2009; 38th anniversary of the Great Plains Blizzard for those who remember!), I stated “there is no coherent MJO”. While not entirely inaccurate, I did underestimate what stochastic forcing represented by the WB (2009) measure of the GWO can do.

Recalling the rapid eastward flows of wave energy through the Eastern Hemisphere subtropical atmospheres per past postings, to keep things “short/simple”, I hypothesize that the seasonal/annual cycle became involved. In other words, the flow of wave energy forced tropical convection to propagate east-southeast into the warm southwest Pacific Ocean. The result was a fading in of a weak MJO signal. As I type, upper tropospheric cross-equatorial divergent outflow from this tropical forcing is leading to an extension of the East Asian jet (discussed below). The astute reader will recall discussions of this possibility were previously given. Yes, a real-time web site with maps and figures would help show these kind of behaviors!!!

Full disk satellite imagery and other tools illustrate a large region of intense to severe tropical rainfall centered ~10S/140E extending from Indonesia to the South Pacific islands. There is evidence some separation is occurring, with one region starting to focus on Indonesia and other ~15S/170E. If there is still any MJO signal, the latter region of enhanced convection would be part of it. Updated through 9 January, per WH (2004) MJO measure retaining ENSO, there was ~1 sigma projection in octant 5 of phase space. Regardless, I do think the Eastern Hemisphere tropical forcing will be dominant during the next several weeks.

In spite of the large global AAM tendency observed late December (calculated tendency ~plus 25 Hadleys), global relative AAM has remained below the R1 data climatology (through 8 January). That tells us the La-Nina base state is “holding” (for reasons). Forcing this large tendency included indirect contributions from zonal mean AAM flux convergence ~35N (with some interhemispheric symmetry) due to the midlatitude baroclinic eddies, and north-south mountains. Perhaps responding to complicated extratropical feedbacks from the South Pacific Ocean tropical forcing (ex., Rossby wave energy dispersions (RWDs) arcing through the North Atlantic Ocean; need maps to show!), even though the global mountain torque signal is decreasing, the East Asian component is ~plus 30 Hadleys. These processes are working to extend the East Asian jet (with an accompanying strong cold outbreak) which will amplify the evil ridge from Hell just off the North American coast next week; a.k.a. the positive phase of the PNA.

Cutting to the chase, I expect to see constructive interference involving various dynamical processes reloading La-Nina during the next several weeks. Many of the components are captured by the WB (2009) measure of the GWO. I am optimistic that the wind and convective signals will remain coupled.

Animations of upper tropospheric daily mean vector wind anomalies present a “distorted” and perturbed configuration of the La-Nina zonally asymmetric spatial pattern for the tropical circulation observed since at least October 2008. There are loose twin anticyclones centered on the Indian Ocean but the cyclones have shifted to 150W. However, divergence is also increasing across the Indian Ocean. I do think by later week-2 into week-3 much of the Indian Ocean into Australia and Indonesia will be strongly active, especially south of the equator. Hence it is likely the twin tropical cyclones will redevelop west of the Dateline.

Global relative AAM tendency is already becoming weakly negative. While there will be variations, that negative tendency may become quite large perhaps forcing AAM to ~2 sigma below the R1 data climatology later this month. Supportive of this notion is zonal mean easterly wind flow anomalies are returning to the subtropical atmospheres, and AAM is starting to flux poleward.

The GWO is slowly completing its 4th orbit in phase space during the last 90 days. While there is currently little projection, per above a shift into octants 8-1 while settling into 2-3 of phase space is probable. The latter has been the 90-day trend, meaning a drift toward the La-Nina attractor. Phase 5 for both the MJO and GWO 250mb snr psi composite anomaly plots loosely depict the current tropical and extratropical circulations, respectively. Phases 8-1 then 2-3 of these plots are the most probable to depict the global circulation weeks 2-4. Synoptically, albeit apparently “delayed” by ~5-10 days (timing always has a noise contribution!), the wicked ridge of the west is likely to discontinuously retrograde perhaps to ~150-160W going into February. That would admit troughs into the western and central USA. During the last few days, week-2 numerical ensembles have been starting to latch-on to this proposed forecast solution.

One of the numerous issues not discussed is that the Northern Hemisphere polar vortex is currently retracted. As the Eastern Hemisphere tropical forcing intensifies, the polar vortex is likely to expand across central and east Asia. However, if not, the East Asian jet may retract so much such that troughs may eventually dig into the Gulf of Alaska ending any possible cold situation across USA. That almost did occur roughly 10 days ago. Having my reasons, I do not think a situation like the 1975-76 USA winter is likely.

Weather impacts per above across the country are already well known. Forced by the oncoming transient +PNA, models have been correctly predicting an Arctic outbreak initially focused Upper Mississippi Valley/Great Lakes starting early next week. That cold air will spread into the eastern states. Care must be taken not to underestimate the ramifications of this airmass given its source. Temperature and precipitation anomalies having similarities to much of December 2008 may then revisit the lower 48 states after ~20 January and persist well into February. That includes the most probable high impact weather from that type of regime.

Dryness is becoming an increasing concern for locations such as California and the southern/central High Plains. As the retrogression occurs starting week-2, it is quite possible the expanded North Pacific Ocean jet will impact most the USA west coast with welcome precipitation for California.

Intense to severe tropical thunderstorm activity will remain generally persistent from Indonesia into the northern Australia for at least the next several weeks. While the South Pacific Ocean will continue to be the “wild card”, some lessening of thunderstorm activity should occur week-1. Much of tropical South America and South Africa may become anomalously active week-1 and perhaps continue week-2. Per above, later week-2 and possibly well into February much of the central and eastern Indian Ocean through Indonesia and Australia may have significant convective enhancement, linked to our quasi-stationary La-Nina regime. I trust the expertise of the appropriate meteorological agencies to alert the public of additional weather hazards worldwide (ex., recent cold in Europe) including official statements for tropical cyclones (ex., Dondo) that are likely to impact regions such as around Australia and Madagascar during the next several weeks.


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 at least an abbreviated discussion on 17 January 2009.

Ed Berry


Linda said...

I am a complete weather novice. I'm concerned about the PDO. I've read that it's in a negative phase and that it will probably remain in a neg phase for at least 5-20 years!!
(I live in Texas and we're in exceptional drought. Drought is made worse in negative PDO)

I got two different sources of raw data for PDO. Both models show a long neg phase from 1944-1978 (30 yr) and long pos phase from 1978-1998. (20 yr)

Data from 1900-1940 seems to be "graphed" as a postive phase, but the raw data shows that it was basically in a "neutral" phase during that time period.

The PDO fluctuated frequently between 1900-1940.

(It seemed to fluctuate as frequently as ENS0.)

I believe the PDO went through a negative phase around July 1998-July 2002. (The last major La Nina) It entered a postive phase from July 2002-August 2005. It then seemed neutral from Aug 2005-Aug 2007. Then, it entered it's current negative phase (with the current La Nina) in August 2007.

Therefore the last PDO cycles lasted only 3 years.

Here is the link to the data:

Some models are forecasting the PDO to be negative for another 20 years.

However, I wonder if this prediction could be somewhat biased?

Are 20 year predictions of the PDO reliable?

Thank You Very Much

Ed Berry said...

Hello Linda,

Thank you for the comment! You are essentially correct about the phase of the PDO based on the available data sets. My understanding is that the current negative phase is the most robust in ~57 years.

In any case, GCM studies show that extratropical SSTs are forced by the tropics, which easily makes sense physically. Another way of understanding this is the tropical SSTs tend to force the atmosphere and vice-versa for the extratropics. The point is a good portion of the PDO is a response to the extratropical circulation that, in turn, is forced by global-scale dynamical processes (such as ENSO variations).

How long this negative phase will persist is unclear. The PDO (like, for ex., the NAO) is red noise, meaning care should be taken attempting to predict it. I certainly agree with your drought concerns, which tend occur in the central/southern High Plains during a low AAM/La-Nina situation.

The following is a link to some PDO stochastic modeling work done folks at ESRL/PSD. You may want to surf around for additional information.

Hope this helps. Please feel free to ask more questions.

Ed Berry

Greg said...

I am relatively new to the avocation of long term pattern forecasting. I read the models such as the GFS, NAM etc. on a regular bases.

I know that you are a busy man, but I have a few question and would be grateful for you to answer them during some of your spare time.

I don't quiet understand the concept of the AAM.

What causes the phases to alternate?
What are the ramifications of the phases (+AAM, -AAM), and what would happen during a phase change?

For example, the global AAM would be a +30 Hadley's in one month, and change to -20 Hadleys in the next.

And lastly, what is R1 Data Climatology?

Thank You Very Much

snoman said...

Hi Ed,

Do you buy the GFS solutions showing a pattern deamplification as opposed to a true PNA retrogression? I am thinking the models are having real problems with the MJO wave that has developed. Also...are you surprised to see such a severe Eastern cold wave with the Pacific in such a favorable state for Western troughing?

Thank you!


Ed Berry said...

Hello Jim,

You are correct about the models struggling with what is likely to be a GWO/MJO 7-8-1-2 transition leading to PNA retrogression. The details are unclear, and maybe until it "practically occurs".

I think the initial westward shift will be linked to the Indonesian forcing, with perhaps a more robust western USA trough once the MJO comes back into the Eastern Hemisphere. The former will be in ~7-10 days with the latter ~week-3. The MJO signal is well into the Western Hemisphere with South America and S. Africa becoming active and the SPCZ shutting down.

I am not at all surprised by the central and eastern USA cold. I did discuss this possibility in earlier postings since I thought our La-Nina would not be as strong as 2007-08. However, I did not anticipate the strength of the current MJO, which has contributed the current cold regime. While currently significantly perturbed, the La-Nina is also a bit stronger than I would have thought.


Ed Berry said...

Hello Greg,

I hope you can attend our GWO workshop to answer some of your questions. It is impossible for me to "educate" in this medium. If you already have not done so, please read our papers and go through the references. A particularly good one is Peixoto and Oort, Chapter 11.

The R1 data climatology is from the first reanalysis data set per Kalnay and others (1996), and goes from 1/68-12/97.

Hope this is helpful.

g said...

Thank you for your response.

I went to search for your recommended article and wow is it long and ambiguous for my impatient and laymen eyes.

I am a much better learner as I go along more than reading, but I will spend a lot of time reading that article in trying to comprehend what it states.

From what I have gathered from your blog, the +PNA ridge is forcing the subtropical and pacific jet up and around the west coast ridge. In tern, this is causing -mountain torque anomalies.

Is this why we the eastern U.S hasn't felt the brunt of La-Nina conditions?

Also, I was looking over the flux convergence reanalysis and it appeared to me that there were positive anomalies in the higher latitudes. Wouldn't this indicate easterly propogation moving poleward and thus an early step for a -NAO?

Thank you for your insights as I find them very interesting.


Ed Berry said...

Hello Greg,

I just posted a discussion. Perhaps that may answer a few of your questions. The +PNA was linked to a strong +East Asian mountain torque, working with the MJO. AAM is starting to flux poleward (zonal mean) across the Northern Hemisphere. That suggests a tilt toward a +NAO (and/or relaxation of the recent negative phase)the next few weeks.