El Nino is a group of warm ocean water temperature. This warm ocean water temperature periodically keeps on developing off the Pacific coast of South America. A phase known as the El Nino Southern Oscillation commonly known as the ENSO refers to the changes in temperature of the surface of the tropical eastern Pacific ocean along with the air surface pressure which is seen in the tropical western Pacific. So during such a time one will see high air surface pressure in the Western part of Pacific. But the mechanism that causes this is yet to be discovered.
We all know that developing nations around the world mainly depend on agriculture, fishing and animal husbandry. And most who are situated on the coast of the Pacific ocean are the ones that are affected the most. El Nino translates as the boy in Spanish. While the more capitalized term El Nino refers to Christ Child. And that is how this whole phenomenon gets its name. The periodic warming in the Pacific near South America is observed during Christmas time, therefore the name El Nino.
El Nino is nothing but the warming in the Pacific ocean sea surface temperature as compared to the average value. The warming is at least 0.5 degree Celsius over the east central tropical Pacific ocean. Generally, this normally happens at irregular intervals, say sometime between 2-7 years, but then it lasts for a period of 9months-2 years. It is observed that the average period it has lasted it about five years. When the warming happens for a period of say 7-9 months it is referred as El Nino condition. But if it exceeds more than that period then it is referred as EL Nino episodes.
So generally the El Nino signs are the walker circulation turns weak but the Hadley circulation becomes strong. Also a rise in the surface pressure over the Indian ocean, Indonesian and Australian ocean is seen. Also the air pressure over Tahiti, the central and the eastern parts of Pacific ocean seems to fall. One will also find the South Pacific trade winds weakening or they start to head towards east, while a warm air will be at rise near the Peruvian regions which will lead to a rainfall in the northern Peruvian desserts.