My recent entry What does El Nino and a Scapegoat have in common? chronicled the plethora of weather events being blamed on El Nino. In terms of Atmospheric Angular Momentum (AAM) and the Southern Oscillation Index that the atmposphere has NOT adopted an El Nino produced circulation.
Now that summer is coming to an end its crunch time. Will the warm water along the equatorial Pacific PUT UP or SHUT UP in its effort to deliver an El Nino. The Nino regions are all in El Nino range and probably have been the source of the El Nino scapegoating still in progress. I am about to demonstrate that the El Nino - looking weather patterns are not being generated by the tropics. My opinion is that high latitude blocking which has ruled the summer generated the repetetive weather patterns APPEARING El Nino-like but not SOURCED by AAM anomalies.
Below is a comparison between AAM anomalies from this year and the previous one. You bee the judge regarding whether an El Nino is clearly underway. Here is 2009:
2008 featured a similar struggle albeit from the 2007-08 strong El Nino lows.
Solar minimum effects and high latitude volcanic activity in the high latitudes have contributed to stronger and more frequent blocking episodes. The inability of the tropics to take control of the weather pattern has likely created a situation which the El Nino looking pattern is being dicated by the extratropics. It certainly is NOT being dictated by the warming NINO regions. Will the extratropics provoke a stable El Nino situation? It can happen but do not count on it.
The Southern Oscillation Index (SOI) is derived from the difference between surface pressure at Darwin, Austrailia and Tahiti. A description of the formula can be found at The Long Paddock.
Here is a comparision of May - September 2008 and 2009 surface pressure observations at the 2 SOI sites. Take note of how September ended in 2008. The 2009 chart ends at Sept 3rd BUT a similar pattern to 2008 may be forming.
Now our tropical atmosphere faces a crossroads. Will a period of La Nina-like trades disperse the El Nino-ish warm anomalies in the Nino zones or could it be that the actual weather really respond to the warmth by lowering the surface pressures from the central equatorial Pacific to the east?
History does teach those who are cheering for an El Nino that a historically cold eastern winter can happen without one.... That is an article coming soon!
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Source Link: examiner.com