What are El Nino and La Nina and it's differences?
El Niño and La Niña are opposite phases of what is known as the El Niño-Southern Oscillation (ENSO) cycle. The ENSO cycle is a scientific term, refers the large-scale fluctuations in temperature between the ocean and atmosphere in the east-central Equatorial Pacific (between more or less the International Date Line and 120 degrees West). El Niño is sometimes referred to as the warm phase of ENSO and La Niña indicates the cold phase of ENSO cycle.
These deviations from normal surface temperatures can have large-scale impacts on ocean processes as well as on global weather and climate. Normally El Niños occur more frequently than La Niñas.
The term El Niño refers to the warm phase of the ENSO. It is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (between approximately the International Date Line and 120 degree West), including off the Pacific coast of South America. El Niño was at first recognized by fishermen off the coast of South America in the 1600s, with the appearance of oddly warm water in the Pacific Ocean. The name El Niño was chosen based on the time of year (during the month of December) during which these warm waters events tended to occur. El Niño is accompanied by high air pressure in the western Pacific Ocean and low air pressure in the eastern Pacific Ocean.
The cool phase of ENSO is called "La Niña" with sea surface temperature in the eastern Pacific (EP) below average and air pressures high in the eastern and low in western Pacific (WP). In the other words, during a period of La Niña, winter sea surface temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest Pacific Ocean. In the U.S, an appearance of La Niña happens for at least 5 months of La Niña conditions. It has extensive effects on the weather in North America, affecting the Atlantic Hurricane Season.
El Niño and La Niña episodes normally last 9-12 months, but some prolonged events may last for years. They begin to form between the months of June & August, reach peak strength during December-April, and then decay between May & July of the following year. While their periodicity can be quite irregular, El Niño and La Niña events occur about every 3-5 years. Systems that cause the oscillation is keep on under study.