|Southern Oscillation Index|
(Aka SOI) The Southern Oscillation is the atmospheric component of El NiIt is an oscillation in surface air pressure between the tropical eastern and the western Pacific Ocean waters. Its strength is measured by the Southern Oscillation Index, which is computed from fluctuations in the surface air pressure difference between Tahiti and Darwin, Australia.
For example, El Nipisodes are associated with negative SOI values, which indicate that there is a relatively small pressure difference between Tahiti and Darwin.
1. El Nipisodes are defined as a sustained warming of the central and eastern tropical Pacific Ocean. This results in a decrease in the strength of the Pacific trade winds, and a reduction in rainfall over eastern and northern Australia.