El Nino and La Nina – Southern Oscillation (ENSO)

The El Nino – Southern Oscillation (ENSO) is a global climatic phenomenon marked by see-saw shifts in air pressure between the Indo-Australian and eastern regions of the Tropical Pacific. El Nino and La Nina refer to extreme phases in the 2-7 year cycle. During the warm ‘El Nino’ phase, the Australian seaboard cools, SE trade winds slacken and extended periods of drought are experienced in Australia. In the cool ‘La Nina’ phase, the seas around Australia warm, the SE trade winds intensify, and widespread rain and flooding occur in Australia. The strength and phase of ENSO is measure by the Southern Oscillation Index (SOI). Consult the Bureau of Meteorology web site for a more comprehensive discussion of ENSO.