Pacific ENSO Update2nd Quarter, 2006 Vol. 12 No. 2 |
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SOI (SOUTHERN OSCILLATION INDEX)During the second half of 2004, the SOI* was persistently negative with an average value of approximately -1.0. This was consistent with weak El Niņo. For the past few months, the SOI has undergone some wild fluctuations with individual monthly index values of -1.1, + 0.3, -4.1, and -0.2 during December 2005, January, February and March 2005, respectively. February's SOI value of -4.1 was the second lowest value of the SOI recorded in over 100 years. The lowest value of the SOI ever recorded was -4.34 in June, 1877. This is just another indicator of the extreme departure from normal of the tropical Pacific climate during February 2005 - it was an extraordinary month by many measures. With the climate expected to continue its slide towards El Niņo Neutral conditions, the SOI should average near zero for the next three to six months, with month-to-month fluctuations within the range of -1.0 to +1.0.
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