El Nino and La Nina
The Sea surface temperatures play a major role in global weather which influences two extreme phases of a naturally occurring climate cycle. I.e., El Nino/Southern Oscillation and La Nina. El Nino refers to the warm phase of the El Nino Southern Oscillation which is called ENSO-that is - El Nino Southern Oscillation. El Nino Southern Oscillation is the cycle of warm and cold temperatures measured on the basis of sea surface temperature of the tropical central and eastern Pacific Ocean. It is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific between the International Date Line and 120°W. It also occurs off the Pacific coast of South America.
Why are they called El Niño and La Niña?
The term El Niño translates from Spanish as 'the boy-child'. Peruvian fishermen originally used the term to describe the appearance, around Christmas, of a warm ocean current off the South American coast. It is now the commonly accepted term to describe the warming of the central and eastern tropical Pacific Ocean. La Niña translates as 'girl-child' and is the opposite ENSO phase to El Niño.
1. The ENSO cycle includes El Nino and La Nina and is the major cause of global changes in both temperatures and rainfall.
2. El Nino is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific.
La Nina –the Cool Phase
1. The cool phase of ENSO is called "La Nina" with sea surface temperature in the eastern Pacific below average and air pressures high in the eastern and low in western Pacific. El Nino is defined by prolonged warming in the Pacific Ocean sea surface temperatures when compared with the average value.
El Nino conditions and El Nino episode
El Niño events are associated with a warming of the central and eastern tropical Pacific.
1. The average period length is five years. When this warming occurs for seven to nine months, it is classified as El Nino "conditions"; when its duration is longer, it is called El Nino "episode".
Effects of El Nino
1. El Nino's warm rush of nutrient-poor water heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the Humboldt Current.
When El Nino conditions last for many months, extensive ocean warming and the reduction in easterly trade winds limits upwelling of cold nutrient-rich deep water, and its economic impact to local fishing for an international market can be serious.
2. El Nino can affect commodity prices and the macro-economy of different countries - and not always for the worst. It can constrain the supply of rain-driven agricultural commodities; reduce agricultural output, construction, and services activities; create food-price and generalised inflation; and may trigger social unrest in commodity-dependent poor countries that primarily rely on imported food.
Hence, we can say El Nino has been used to explain unusual climatic changes across the globe. But, modern climatology taken into account various other phenomena also. However, It has far-reaching and varied effect on climate across the world.El Niño and La Niña events are a natural part of the global climate system. They occur when the Pacific Ocean and the atmosphere above it change from their neutral ('normal') state for several seasons.