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El Nino Comparisons - Some Thoughts on Winter

By Joe D'Aleo
Monday, September 28, 2009

This El Nino is still taking shape and looking like a weak to at most a moderate event. Note the September 20th 5-day cross section here.



These cross sections show you the temperatures and temperature anomalies with depth across the equatorial tropical Pacific from west (140E) to east (100W) derived from TAO Triton buoys. Eastern areas have suffered from data dropout from vandalism.


See how the warm plume has consolidated a little but not intensified much since a month earlier.



Let’s compare to some recent El Ninos in September. The most recent event was in 2006/07. It looked similar. It peaked in January and then diminished rapidly giving way to a strong La Nina by the following winter/spring.


2002/03 was a much stronger event already in September. It went on to a December peak as a moderate event with a slow decline with warmer water consolidating over the central Pacific .



The event was weaker than the super El Nino of 1997/98 which had very large anomalies at this time of year.



El Nino of 1994 was more similar to this September.



The SOI has never fully engaged on this El Nino. Shown in purple it is second weakest, only trailing 1963 at this early date.



Ocean heat content has back off the peak set in July.




The El Ninos and La Ninas tend to cluster in decadal periods with the entire Pacific basin taking on El Nino or La Nina like configurations. This is called the Pacific Decadal Oscillation or PDO.



When the Pacific is cold in the mean as it was from 1947 to 1977, La Ninas dominate as shown by the chart above with blue spikes representing La Ninas and red El Ninos. When it is warm as it was from 1977 to 1997, El Ninos dominate as was the case from 1977 to 1998.


That doesn’t preclude the opposite state from occurring but they tend to be weaker and briefer. Since we are now in the cold PDO, we might expect this La Nina being like those in the 1947-1977 period and after 1998. 


Since our overall ocean and solar cycles suggest similarity to the late 1950s to early 1960s, two years for which we DON’T have cross section data for but which were El Ninos coming off La Ninas during a quiet sun were 1963/64 and 1965/66. The winters that followed were cold with typical El Nino nor’easters. 



The NAO has tumbled in the last few summers and if this continues through or returns the winter, it would help ensure this cold winter.



The combination of higher aerosols in polar region was shown by Oman (2006) to be followed by more high latitude blocking. This summer we had a new record for June and July for the lowest AO and second lowest NAO for the summer.



The cold 1960s winter were due to a combination of low solar AND high stratospheric aerosols which combined with a cold Pacific and cooling Atlantic. Our stratospheric aerosol levels are not as high but our solar levels are lower than the 1960s.


The ENSO models compiled by IRI in September. Most models peak the El Nino late this year as we saw in 1963/64, 1965/66..



The solar of course is at the lowest levels it has been since the early 1900s. Eventually it will pick up, but the question is when and how high. Most forecasts have been updated with delayed and reduced maxima. NCAR remains the sole resistance having yet to discard their model that had one of the strongest cycles on record peaking in a couple of years. Sorry guys. Not this time.


In upcoming weeks, we will have a more detailed look at the winter ahead.