It is the cold counterpart to El Nino. La Niña is characterized by unusually cold ocean temperatures in the Equatorial Pacific, compared to El Niño, which is characterized by unusually warm ocean temperatures in the Equatorial Pacific.
The coupled atmosphere-ocean phenomenon known as El Niño is frequently followed by a period of normal conditions in the equatorial Pacific Ocean. Sometimes, but not always, El Niño conditions give way to the other extreme of the El Niño-Southern Oscillation (ENSO) cycle. This cold counterpart to El Niño is known as La Niña, Spanish for “the girl child.”
La Niña is defined as cooler than normal sea-surface temperatures in the central and eastern tropical Pacific ocean that impact global weather patterns. La Niña conditions recur every few years and can persist for as long as two years. It can be thought of as the opposite of el nino. Both terms refer to large-scale changes in sea-surface temperature across the eastern tropical Pacific. Usually, sea-surface readings off South America’s west coast range from the 60s to 70s F, while they exceed 80 degrees F in the “warm pool” located in the central and western Pacific. This warm pool expands to cover the tropics during El Niño, but during La Niña, the easterly trade winds strengthen and cold upwelling along the equator and the West coast of South America intensifies. Sea-surface temperatures along the equator can fall as much as 7 degrees F below normal.
Typically, a La Niña is preceded by a buildup of cooler-than-normal subsurface waters in the tropical Pacific. Eastward-moving atmospheric and oceanic waves help bring the cold water to the surface through a complex series of events still being studied. In time, the easterly trade winds strengthen, cold upwelling off Peru and Ecuador intensifies, and sea-surface temperatures (SSTs) drop below normal. During the 1988- 89 La Niña, SSTs fell to as much as 4 degrees C (7 degrees F) below normal. Both La Niña and El Niñq tend to peak during the Northern Hemisphere winter.
Unlike El Nino, which is described as having atypically warm ocean temperatures in the Equatorial Pacific, La Nina harbors atypically cold ocean temperatures in this same region and occurs less frequently.
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