SOUTHERN OSCILLATION INDEX (SOI)

The 3-month average of the Southern Oscillation Index for the 2nd Quarter of 2010 was +0.7, with monthly values of +1.2, +0.8, and +0.1 for the months of April, May, and June 2010, respectively. The recent shift from negative SOI values to positive values during the first half of 2010 is consistent with a shift from El Niño to La Niña in the ENSO cycle.

*Note: Normally, positive SOI values in excess of +1.0 are associated with La Niña conditions, and negative SOI values below -1.0 are associated with El Niño conditions. Low SOI values suggest a weak coupling between the ocean and the atmosphere. The SOI is an index representing the normalized sea-level pressure difference between Darwin, Australia and Tahiti, respectively. The historical record of the SOI from 1866 to present was calculated based on the method given by Ropelewski and Jones (1987). The complete table can be found at http://www.cru.uea.ac.uk/cru/data/soi.htm.