El Niño Southern Oscillation (ENSO)

El Niño Southern Oscillation (ENSO)

The relationship between El Niño and the Southern Oscillation. An El Niño episode begins when the weakening of the surface air pressure gradient between the western and central tropical Pacific heralds and the slackening of the trade winds.

Southern Oscillation

A seesaw variation in air pressure across the tropical Indian and Pacific Oceans.

El Niño vs. La Niña

El Niño

Anomalous warming of surface waters in the eastern tropical Pacific and along the equator; accompanied by suppression of up-welling off the coasts of Ecuador and northern Peru and along the equator east of the international dateline. Typically lasting for 12 to 18 months and occurring every 3-7 years. El Niño is accompanies by changes in oceanic and atmospheric circulation plus weather extremes in various parts of the world.

La Niña

The episode of particularly strong trade winds and unusually low sea-surface temperatures (SST) in the central and eastern tropical Pacific; essentially the opposite of El Niño. La Niña is accompanied by weather extremes in various parts of the world.