El Niño-Southern Oscillation

Definition: The El Niño-Southern Oscillation (ENSO) is a ocean-atmosphere event that involves sustained sea surface temperature fluctuations in the Pacific Ocean that result in climate perturbations such as floods and droughts in widespread regions. ENSO involves two sea surface trends, El Niño and La Niña. El Niño is a warm current that originates in the tropics and each winter intrudes into the cooler waters that hug the west coast of northern South America. El Niño carries with it nutrient-poor tropical water. The La Niña current often occurs after the El Niño event and is characterized by warm water being displaced further to west than normal.