El Niño–Southern Oscillation definition

Summary

El Niño–Southern Oscillation (ENSO) is a recurring global climate phenomenon caused by linked variations in tropical Pacific Ocean sea-surface temperatures, atmospheric pressure, and winds. It affects climate across the tropics and subtropics and has teleconnections that influence weather in higher-latitude regions. ENSO occurs in three phases: neutral, El Niño, and La Niña. El Niño is the warm phase, characterized by unusually warm sea-surface temperatures in the central and eastern tropical Pacific, weakened trade winds, reduced coastal upwelling, and shifts in rainfall and atmospheric circulation. La Niña is the cool, generally opposite phase, with unusually cold eastern and central Pacific waters, stronger trade winds, and enhanced upwelling. The atmospheric pressure variation associated with these ocean changes is called the Southern Oscillation. ENSO phases typically last about a year, recur irregularly every two to seven years, and can disrupt weather patterns worldwide.

Key Points

• 1

  ENSO is a coupled ocean–atmosphere climate phenomenon centered in the tropical Pacific Ocean.

• 2

  It has three phases: neutral, El Niño, and La Niña.

• 3

  El Niño involves warming of the central and eastern tropical Pacific, while La Niña involves cooling in those regions.

• 4

  The Southern Oscillation is the atmospheric component, involving changes in surface air pressure between the western and eastern tropical Pacific.

• 5

  ENSO influences global rainfall, temperature, storms, droughts, and other weather patterns.