TomC, you have to see how accurate the forecasts actually are to make that statement. I've been watching this for a long time and you can't put much stock in the model forecasts.
The NOAA/CPC's own report notes they missed the 2006 El Nino and the rapid transition to La Nina in 2007.
How about the double-dip 2008 La Nina. Nope, they were predicting an El Nino to develop in 2008.
And the 2009 Moderate El Nino. Well, they started to pick that one up by May 2009.
And the currently rapidly developing La Nina. They are only starting to forecast a large one in the last few months and they are predicting -2.0C in July 2010 and there have only been 4 La Ninas to get down to that level. Their Jan 2010 forecast for July was +1.0C so that is not good. I was already calling La Nina last November.
Edited by user 24 June 2010 19:37:14(UTC) | Reason: Not specified
Bill, in your opinion, how is this La Nina going to compare to previous events?
I posted that exact same ensemble forecast in my last post on the previous page. The IRI has an archive of forecasts as well if you want to look through it.
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To Gavin P
This La Nina will be the biggest one yet - lower than -2.5C
The best predictors months in advance are the following.
This should trend down for another 4 months and the Nino 3.4 index will be about the same number about 1 month later.
The next best predictor is Atmospheric Angular Momentum which is currently at almost the lowest value it has ever gotten to since measurements began in 1958. Nino 3.4 follows the trend of AAM very closely as well. AAM drives the Trade Winds which drive the circulation of the equatorial pacific. The tendency metric used for AAM projects it to fall below -3 (e+25) in the near future.
Or one can also use the average of these three bouys at 100M depth (which leads the Nino 3.4 Index by about 3 to 6 months - the lead time depends on the strength of the Trade Winds and AAM)
-4.0C, http://www7320.nrlssc.navy.mil/global_nlom32/navo/z0n140w.gif
-5.0C, http://www7320.nrlssc.navy.mil/global_nlom32/navo/z2n140w.gif
0.0C, http://www7320.nrlssc.navy.mil/global_nlom32/navo/z2s140w.gif
Edited by user 25 June 2010 00:54:56(UTC) | Reason: Not specified
Thanks Bill. The coldest/most intense La Nina on record would be pretty shocking. What would be the global effects of a mega La Nina? Clearly for a lot of places it'd be
Edited by user 25 June 2010 09:49:57(UTC) | Reason: Not specified
...
I don't know ENSO history that well, so, Bill, when you say 'biggest yet' you mean since when?
But, I'll try to keep a copy of your prediction just to see how you do . Fwiw, I've no idea what magnitude any coming LN is but I'd be surprised, because such things are surprises, if it's the strongest on record
Technically, I don't have any special insight into what it is going to happen either but I've been making too many pronouncements on the state of the things to not put something out there (and I shouldn't be downplaying the agency ENSO forecasts without a having a forecast/guess as well).
CFS now going for a very strong La Nina by autumn;
http://www.cpc.ncep.noaa.gov/products/people/wwang/cfs_fcst/images3/nino34SSTMon.gif
Average goes down to around -2 by around November
Region 4 drops to around -1.5 by winter;
http://www.cpc.ncep.noaa.gov/products/people/wwang/cfs_fcst/images3/nino4SSTMon.gif
Interestingly this looks like a west based La Nina, with regions 1 and 2 seeing a marked warming back to neutral by late autumn;
http://www.cpc.ncep.noaa.gov/products/people/wwang/cfs_fcst/images3/nino12SSTMon.gif
Anybody know how west based La Nina's would typically compare to east based La Ninas?
Edited by user 02 July 2010 12:58:01(UTC) | Reason: Not specified
One of the features of a La Nina or an El Nino is that the surface Ocean Currents in the Equatorial Pacific either speed up (La Nina) or slow down or even go backwards (El Nino). The normal direction is a moderate East to West. [The anomaly patterns extend downward to 200 metres so it is not just surface currents, although directions may be opposite as one goes deeper].
In May and June 2010, the Current was well above normal by as much as 0.5 Metres/sec.
This map shows the ocean Current anomalies at 15 metres depth. Blues and Purple are anomalies flowing East to West (while the Reds are anomalies flowing to the East).
The last two months are about as high La Nina-type ocean currents as there has been in the record.
Here's May 2010
Here's is what the Currents looked like at the peak anomaly in the 1997-98 El Nino.
Edited by user 02 July 2010 14:18:19(UTC) | Reason: Not specified
One of the features of a La Nina or an El Nino is that the surface Ocean Currents in the Equatorial Pacific either speed up (La Nina) or slow down or even go backwards (El Nino). The normal direction is a moderate East to West.
Are these currents wind driven Bill? What I am thinking of, are the sub tropical high pressure zones moving equatorward in response to the jetstreams (at least in the N. Atlantic)moving equatorward and squeezing the easterly winds into a narrower band and cooling the oceans on the way?
They are wind-driven (although part of it is just the way the ocean organizes itself based on geography, temperature, salinity and the fact the Earth is rotating). The n. Atlantic doesn't enter the picture other than a very, very small influence related to Atmospheric Angular Momentum
The question is what drives the Equatorial Pacific winds? What makes them stronger or lighter? It appears to just be one big inter-related system and all the parts of it work together in an oscillation, sometime self-reinforcing, sometimes pushing the oscillation back in the other direction.
El Nino, then neutral, then La Nina back to El Nino and so on.
An oscillation back to an El Nino pattern is now setting up for next year.
I think this animation of clouds and winds (every hour over 1 full year) produced by UCAR, provides the best explanation for how the climate really works that I have seen. It is partly model-based, partly based on actual data collected over many years.
It is a big file, sometimes loads a little slow. Hope it works.
https://www.ucar.edu/publications/nsf_review/animations/ccm3.512x256.mpg
On the right track and asking the right questions
I don't see the answer as lying exclusively with the oscillations within the oceans or exclusively with the variability from the sun. One needs both influences in a constant interplay to explain observations.
The recent El Nino matched El Ninos of similar strength that occurred during the warming spell of the late 20th century but it failed to push the jets so far poleward. The most obvious change since the late 20th century is the less active sun so one needs to propose that a less active sun enhances the polar oscillation negatively thus pushing the jets equatorward and resisting any poleward pressure from warmer ocean surfaces.
The outcome of the interplay between the solar and oceanic influences acting on the latitudinal positions of the jets and the ITCZ results in changes to the surface winds and thus affects the relative frequency and intensity of the subsequent El Nino or La Nina events.
The ENSO cycle has a profound efect on global air temperatures but it's character at any given time is an outcome of independent oscillations in oceans and air driven by internal oceanic and external solar influences respectively and interacting in the equatorial regions.
That should be easy to demostrate or rebut from continuing observations. We need to observe the way the jets and the ITCZ move latitudinally in response to changes in equatorial sea surface temperatures and changes in solar surface variability. However I think one needs at least 30 years to discern the pattern from interannual and decadal 'noise' in the system.
The pattern is very clear to me on a 500 year cycle from MWP through LIA to date and is clear but less obvious on timescales of about 3 decades. It is not so clear on timescales of less than 30 years due to internal system chaotic variability.
In the Arctic Ice thread Beng, today, mentioned GLAAM - a term I'd not come across before. Googling, the first description I came up with was this - (Dated May 25)
With a La Nina beginning to unfold, one index we need to watch is the globally averaged atmospheric angular momentum (GLAAM). All of the other major indices that are critical to ENSO are in a La Nina state now, but the GLAAM continues to be in the positve El Nino state. IMO if this index goes persistently negative we will have a significant cold ENSO event.The GLAAM measures the overall momentum of the entire atmosphere of the Earth. Negative GLAAM indicates an easterly anomaly which is favorable for enhanced trade winds in the tropics. If the GLAAM remains positive, I would have to guess the ENSO will settle into a cold neutral or maybe weak La Nina state.from -http://westernusawx.info...ndex.php?showtopic=29946" href="http://westernusawx.info/forums/index.php?showtopic=29946">http://westernusawx.info/forums/index.php?showtopic=29946
This describes pretty well what I was trying to describe. The next question then, is, how does the strength of the trade winds including GLAAM, respond to the position of the jetstreams? - any experts out there?
I think what you describe is, with reasonable historical data and rescources to do the research, demonstrable now
http://westernusawx.info/forums/index.php?showtopic=29946
I don't have evidence to back this up, but here's what I'd expect; if the jets are pushed closer towards the equator, then more energy is trapped around the tropics which ought to lead to a stronger pressure gradient and stronger trade winds. I guess the implication of this is that if a weak solar signal does indeed produce increased blocking in polar regions, pushing the jets south, then it could produce stronger trades in the tropics, increased trade winds and increased upwelling of water off the coasts of South America and Africa.
Of course it's not that simple though since you'd also then expect some kind of negative feedback to kick in due to reduced tropical heat as a result of the original cold upwelling. Perhaps the overall result would be stronger la nina events and weaker el ninos? - but total speculation on my part.
:)