El-Nino, La-Nino and their Effects


By: Mohit Diwan


What is El-Nino?

El Nino means The Little Boy and is often called “a warm event”. El Nino is an oscillation of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe. In general, El Nino is defined by prolonged warming in the Pacific Ocean sea surface temperatures when compared with the average value. The consequences are increased rainfall across the southern tier of the US and in Peru, which has caused destructive flooding, and drought in the West Pacific, sometimes associated with devastating brush fires in Australia.


La Nina means The Little Girl and is sometimes called El Viejo, or simply “a cold event”. It is the climate counterpart to El Nino and is defined by cooler-than-normal sea-surface temperatures across much of the equatorial eastern and central Pacific.

El Nino is characterized by unusually warm ocean temperatures in the Equatorial Pacific, as opposed to La Nina, which characterized by unusually cold ocean temperatures in the Equatorial Pacific. An El Nino is associated with high pressure in the western Pacific, whereas a La Nina is associated with high pressure in the eastern Pacific.

The ‘see-sawing’ of high pressure that occurs as conditions move from El Nino to La Nina is known as the Southern Oscillation (SO); the atmospheric component of El Nino. The strength of the Southern Oscillation is measured by the Southern Oscillation Index (SOI); which is based on a long record of pressure measured by two stations: Darwin (Australia) and Tahiti. The often used term El Nino-Southern Oscillation (ENSO) is a coupled system, meaning the atmosphere and ocean influence each other. ENSO affects the sea surface temperature (SST) in regions where fishing is a major industry to some countries.

The last extreme El Nino, in 1997—98, resulted in the hottest year on record, and the accompanying floods, cyclones, droughts and wildfires killed an estimated 23,000 people and caused £21bn—£28bn in damage, particularly to food production and also caused the worst coral bleaching in recorded history. In total, 16 per cent of the world’s coral was lost and some countries like the Maldives lost up to 90 per cent of their reef coverage.

This could spell disaster for the Coral Triangle, a south-east Asian bioregion that’s the underwater equivalent of the Amazon, home to more marine species than anywhere else on Earth. The Coral Triangle sees prolonged periods of temperature anomaly during an El Niño because the equator passes through the middle of it, so it experiences both northern and southern hemisphere summers.

(Source: www.climate.gov)

(Source: www.climate.gov)

India is expected to be the first to suffer, with weaker monsoon rains, followed by further scorching droughts in Australia and collapsing fisheries off South America. But some regions could benefit, in particular the U.S., where El Nino is seen as the “great wet hope”, bringing rains that could break the searing drought in the west.


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