El Niño and La Niña are changes in the winds and ocean currents of the tropical Pacific Ocean that have far-reaching effects on global weather patterns. Together, El Niño and La Niña are extremes that make up a cycle called the El Niño Southern Oscillation (ENSO). An oscillation is a repeated movement or time period. El Niño and La Niña events do not occur in a regular or seasonal pattern; instead, they repeat about every two to seven years and last for a few months.

How El Niño and La Niña Occur

El Niño events occur when the trade winds and equatorial current south of the equator in the Pacific Ocean lessen in intensity. The trade winds, or trades, are strong, steady...