Friday, July 03, 2009

Brief Update on a Bearish Atmosphere

"The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”

Time constraints preclude a complete discussion. In fact, at this point that may be case for at least the rest of this summer. The 6 June 2009 posting has all relevant links. I will attempt another short writing the weekend of 11-12 July.

SSTs across the equatorial Pacific Ocean basin remain above normal, generally ~0.5-1C, with localized greater magnitudes west of South America. Additionally, latest TAO buoy data of 5-day averaged ocean surface waters indicate that the 29C isotherm on the equator is at about 165W, the farthest east in at least 2 years. Further, there is a separate warm anomaly along and just west of the Dateline with totals in excess of 30C. However, the subsurface anomalies in this region, while deep (~200m), are only plus 1-2C. I can easily attribute much of the central Pacific Ocean warming to strong interactions with the extratropics, including the weakened trades and actual westerlies.

The wind and convective signals are seemingly wanting to drift away from the EL-Nino attractor in WB (2009) GWO phase space (see ALL plots). Total AAM including the mass (earth) term through 30 June has dropped to more than 1 sigma below the R1 data climatology. Contributing processes include the following. As part of a dynamic response to interhemispheric meridional symmetry of zonal mean zonal wind anomalies, zonal mean low pressure anomalies are present ~35N and 45S. There has also been strong frictional dissipation of intense westerly wind flows across the Southern Hemisphere storm track regions. Should total AAM departures become comparable to that observed during this past January and February, my concerns of an El-Nino "false alarm" for the weather-climate dynamical system will be significantly raised.

Finally, responding to the global wind signals while also part of complex feedback processes (interactions with baroclinic wave packets, RWDs, etc.), strong tropical convective forcing has returned to the North Indian Ocean as well as the Eastern Hemisphere monsoon systems. A weaker but important region of convection is also present ~0/160E. Hence our nemesis of 2 areas of tropical forcing is back (other global regions understood). Furthermore, there has been some westward shifting of these regions of enhanced tropical rainfall, especially across the Indian Ocean. Which will dominate going into boreal autumn?; stay tuned. The bottom line is that the global wind and convective signals continue to lead the SSTs (broken record), and the ENSO situation is unclear (will stochastic forcing have giveth then taketh away?).

A loose superposition of the snr plots for GWO/MJO phases 8-1-2 (considering synoptic variations) still depict the global atmosphere for all fields. I suspect that will be true the rest of the summer, including the USA July trough-ridge-trough pattern possibly transitioning to more of a western trough and southeast states ridge situation during August.

Ed Berry

17 comments:

snoman said...

Hi Ed,

Looking at the subsurface animation, there appears to be a slow dissipation of the warm anomalies west of 160W, but a continued warming above 100 meters east of 160W. All in all it looks like a slow response to the recent strong trade winds, but with no WWB's in sight we could see neutral ENSO by the end of summer.

This will be a fun one to watch!

Jim

Greg said...

HP is starting to build in the C PAC. Say it isn't so, I don't want to see my Nino go.

Decent -OLR anomalies are building between 65E and 90E, and the MJO signal is resurging in the W PAC. Is it safe to say that the E PAC will see SST anomalies go negative in the next 1-2 weeks?

The whole Rossby wave thing is still a mystery to me since there are multiple types.

Regardless, this will be very interesting to watch over the next 1-2 months.

snoman said...

No question that anomalous nigh pressure over the north central and northeast Pacific is very bad news for an El Nino. It appears the positive anomalies will drift north over the next week or so. After that the GFS and its ensemble want to put an anomalous ridge over the central Pacific once again. If so, it would appear the El Nino has simply given up.

The MJO ensemble forecast continues to indicate a re-emergence of the MJO in octant 1. Another very unfavorable note for El Nino. Finally the surface pressure forecasts for the central equatorial Pacific indicate a round of healthy trade winds and another period of high SOI in the coming days. In my opinion another big thing to watch will be for a return of anomalous high pressure to southern West Coast of South America. That would be yet another sign the El Nino has thrown in the towel.

Jim

Captain Climate said...

To El Nino or not ... That is the question. Another return to a La Nina base state (not a given at this point) should raise concern of continued cooling. Too bad Washington DC and NY are in regions which often benefit by warmer, drier winters in STEREOTYPICAL situations.

The heart of the scientific method is to prove the null hypothesis. In our case this means skepticism of a circulation regime change until we see evidence that the old pattern has resolved.

More than last summer, the El Nino resembling activity seems to be the low AAM pattern reloading. Perhaps an extra-tropical driven El Nino is just a fake?

It is funny that as the AAM ramp up had reached a crescendo ... POOF!!! its gone?

Sorry for writing a novel. Thanks for everything Ed!

Captain Climate said...

Clarification: This summer's Bull Run seemed to exceed last year BUT maybe the Bull needs real horns to gore the Bear....

PricklyPear said...

I found this blog when I was searching for an explanation for the hows and whys of weather.

I was specifically looking for something about "equilibirium".

Something based on the old concept that energy is neither created or destroyed, it just moves around.

When I read about AAM, a light bulb went on.

I don't understand the technical details. But the general concept makes sense to me.

Ed Berry said...

Hello all,

Again, thank you for the input! All we can do is tilt the odds slightly toward a continuation of the warm event going into boreal winter. However, the ENSO situation is unclear, and the period of OND may be extremely critical.

Ed

snoman said...

Hi Ed,

Do you think the surface pressure gradients and anomalies along the West Coast of South America play a significant role in ENSO SST's? I know the SOI* (not SOI) is partially derived from surface pressure anomalies at 30S / 95W.

I ask this because one of the things I monitor regularly is the surface pressure off the central West Coast of South America and it is about to go bonkers according to the latest models. The pressure in that region has been quite negative lately, and I believe this dramatic shift could be another sign this El Nino isn't healthy. The wind predication models show a very favorable profile for significant upwelling off the coast of Peru very soon.

Jim

Greg said...

Hey snoman,

I'm no Ed Berry, but wouldn't an area of HP in the southeastern PAC introduce increased easterlies, and therefore almost automatically play a significant role in SSTs if it remains persistent? Thinking through this logically, if HP is to exist in C South America, then LP would exist to the north of that in either Central America, or northern South America (SA). HP would then be to the west of that in the central equatorial Pacific. As I'm sure you know, that would cause a lot of problems. But then again, this isn't exactly the most scientific method of what role HP would have in C SA.

I saw the GFS forecast that setup in the next 3 days. I'm still working on connecting the AAM budget to actual processes, but the latest Relative AAM has propogated strong easterlies to around 50S~70S, so I do think the GFS is to be believed with the strong area of HP moving in.

snoman said...

Greg,

Good points! I think the strong winds blasting up the coast of SA should cool the SST's dramatically off the coast of Peru which could wreck some real havoc with the Nino. The surface wind maps show those winds connecting with an unbroken zone of trade winds all the way to about 170E. Furthermore, strong surface high pressure over the NE Pacific will be feeding some nice trades in from north of equator.

On another note both the 30 day and 90 SOI are about to go positive again.

Jim

Ed Berry said...

Greg,Jim and others,

Thank you for the dialog. Again, monitoring is critical. The basin wide equatorial Pacific warming is probable to continue at least into fall. The west coast SA HP you are all referring to does have some linkage(RWDs)to the North IO forcing, and MAY not be favorable to sustain the above mentioned warming. Regardless, ENSO is an interannual variation of the global weather-climate dynamical system, not just the eq. Pacific Ocean. Right now, the global wind and convective signals are not entirely in sync with an El-Nino, and we will see what happens during OND.

Ed

snoman said...

Very interesting stuff going on! The GLAAM is already negative and the tendency is falling again. Besides that the Darwin / Tahiti gradients seem to be going toward another high SOI period.

As a fan of neutral or cold ENSO, I am feeling better by the day! Still a long way to go, but the atmosphere seems to be unwilling to perpetuate the El Nino.

Jim

Captain Climate said...

Mr. Snoman, we share a dream (bung, bung, bung, bung)
This winter might bring snow and cold like we've never seen ....(bung, bung, bung, bung)
Give AAM Volatility and (High Latitude Blocking ability!(bung, bung, bung, bung)
Then we will see that weak eastern winter days are over.
Snoman, don't keep all the cold!
Can't everybody get a winter to call their own
Please share some winter....
Mr. Snoman, bring me a dream....

Dean

PS: To the tune of the Chordettes "Mr. Sandman".

snoman said...

Hi Dean,

I agree! There could certainly be enough winter to go around this time. I read soemthing about this being the latest spring around Hudson's Bay since 1962. As you likely know Jan 1963 was historically cold for the United States as a whole. The above normal heights in the Arctic have been very predominant for a long time now.

Certainly a good chance this winter will feature some mondo blocking episodes. My big worry was an El Nino would screw up the West, but that appears rather unlikely now. The atmosphere is very reluctant to allow an El Nino right now.

Jim

snoman said...

Another interesting tidbit is the fact the Earth AAM has been low for a good period of time. According to the Earth AAM records it used to run much lower in the 1950s, 60s, and 70s than it has recently. Seeing it and the GLAAM low at the same time is pretty exciting.

I seem recall Ed once saying those old Earth AAM records may not be accurate though. If the records were accurate, perhaps the Earth AAM hold some of the key as to why the winters used to be so much colder and more blocked.

snoman said...

The 200mb zonal wind index is now positive.

Another sign the El Nino is closer to being doomed.

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