La Niña is defined as an oceanic-atmospheric phenomenon wherein water temperatures in the Equatorial Pacific Ocean become cooler than normal. La Niña conditions occur on an average every 3 to 5 years and can persist for as long as two years. La Niña impacts global weather patterns.
What is the difference between El Nino and La Nina?
Both El Niño and La Niña are extreme phases of a naturally occurring climate cycle. These two terms refer to large-scale changes in the sea surface temperature across the eastern tropical Pacific.
Normally, the sea surface temperatures off South America's west coast range from the 15 to 25 degree Celsius. On the other hand, they exceed 26 degrees Celsius in the "warm pool" located in the central and western Pacific.
Also read, What is El Niño
During El Niño years, this warm pool expands to cover the tropical regions. The exact opposite happens during La Niña, wherein the easterly trade winds strengthen and the cold upwelling along the equator and the West Coast of South America intensifies. The sea surface temperatures along the equator could then fall by 7°F (-13.88°C) below the normal levels.
Why do El Niño and La Niña occur?
The interaction between the surface of the ocean and the atmosphere in the tropical Pacific leads to El Niño and La Niña conditions. Simply put, El Nino and La Nina are oceanic-atmospheric phenomena, leaving inexplicable mysteries.
Just as changes in the ocean impact the atmosphere and global climate patterns, even changes in the atmosphere impact the ocean temperatures and currents. This is a recurring phenomenon, oscillating between warm (El Niño) to neutral (or cold La Niña) conditions.
What causes La Niña?
La Niña conditions are followed by a buildup of cooler than normal subsurface Ocean waters in the tropical Pacific.
The atmospheric and oceanic waves travelling eastwards help in bringing the cold water to the surface through a complex series of events.
Gradually, the easterly trade winds strengthen and the cold upwelling off Peru and Ecuador intensifies. Ultimately, the sea-surface temperatures (SSTs) drop below normal levels. Records suggest that during the 1988-89 La Niña episode, the SSTs fell 4°C or 7°F below normal.
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