What is El Nino ?
Literally meaning 'little boy' in Spanish, El Nino is an atmospheric phenomenon which causes water in the equatorial Pacific to warm up abnormally due to weakening of trade winds. There are periodic warming and cooling of vast stretches of ocean surface. During El Nino years, the Pacific warm pool expands to cover the tropical regions.
When does El Nino occur ?
It is a cyclic process where weather system re-emerges after a gap of about 2 to 5 years in the Pacific Ocean and its effect last for about 12 months on an average. Normally the sea surface temperature off South American west coast ranges from the 15°C to 25°C. It exceeds 26°C in the 'warm pool' located in the central and western Pacific. El Nino occurs when the threshold value of 0.5°C of ocean Nino index is met or crossed for a minimum of five consecutive overlapping sessions of 3 months each.
Impact of El Nino on Indian Monsoon
El Nino or the warming of sea surface temperatures affect winds pattern and trigger both flood and drought in the different part of the world. Such an event is usually characterized by Extreme weather events in many parts of the world. A few places across the globe also get benefit from El Nino.
El Nino effect rainfall during the monsoon months. Trade winds blow westward from South America toward Asia during Indian monsoon months. Warming of the Pacific result in the weakening of these winds. Moisture and the heat content thus, get limited and result in reduction and uneven distribution of rainfall across the Indian sub-continent.
The most prominent drought in India, in recent year have been the El Nino triggered drought, in 2002 and 2009. During and El Nino, monsoon never witnesses excess rainfall bring up few exceptions. For instance, 1997-98, when El Nino did not cause drought in India.What is LA Nina ?
La Niña means The Little Girl in Spanish. La Nina is an oceanic-atmospheric phenomenon that causes the water temperature in the Equatorial Pacific Ocean become cooler than normal. La Nina occurs on the average of every 3 to 5 years and can persist for as long as of 2 years. Naturally it impacts Global weather patterns.
Causes of La Nina
La Nina occurs when easterly trade winds intensely bring cold water to the surface through a complex series of event along the equator in the tropical Pacific off Peru and Ecuador on the west coast of South America. The sea surface temperature along the equator could then fall by -13.88°C below the normal levels. Record suggest that during the 1988-89 La Nina, the sea surface temperature fell below 4°C below normal.
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