El Niño and La Niña

El Niño is a weather event involving the eastward migration of a mass of warm water normally found in the western equatorial Pacific Ocean.

Periodically (usually every three to seven years), the easterly trade winds in the Pacific weaken and allow the pool of warm water to drift from Australia to the western coast of South America, often triggering heavy rains there.


This vast pool of warm water is thought to set off a chain reaction that can affect jet stream and weather patterns around the world, especially in the winter months in the northern hemisphere. El Niño is sometimes referred to as ENSO for El Niño–Southern Oscillation. The Southern Oscillation is a seesaw of air pressures on the eastern and western halves of the Pacific.

La Niña is essentially the opposite of El Niño. La Nina is a migrating pool of cooler-than-usual ocean water. The cool water can suppress rain-producing clouds, which leads to dry conditions.

Peruvian fishermen first noticed the effects of a new El Niño at Christmas ime, when storminess off the coast reduced the supply of fish. "El Niño" is Spanish for "the boy child," and is used to refer to the Baby Jesus. The name La Niña ("the girl child") was coined to deliberately represent the opposite of El Niño.

Because even the most dedicated scientists do not thoroughly understand El Niño and La Niña (we do not know, for instance, why the trade winds suddenly die down and allow the warm water pool to move eastward), we can only describe certain tendencies in the weather.

In the past, El Niño has often brought heavy rains to southern California and to a portion of the South from Atlanta to Cape Hatteras; it can bring relatively mild winter temperatures to the northern third of the country. However, these effects are not consistent in every El Niño event on record.

The stronger the La Niña, the more severe the droughts. Tha La Niña in 2009 is creating severe drought in much of the world, causing an agricultural crisis.


El Niño

The data from TOPEX/Poseidon, and in the future Jason-1, helps us study and understand the complex interactions between the oceans and the atmosphere which affect global weather and climate events. One well-known example of this interaction is an El Niño event.

El Niño was named by people who fish off the western coast of central America to refer to the warm current that invades their coastal waters around Christmastime. El Niño events disrupt fisheries and bring severe weather events worldwide.

In a normal year, the trade winds blow westward and push warm surface water near Australia and New Guinea. When warm water builds up in the western Pacific Ocean, nutrient-rich cold water comes up off the west coast of South America and fosters the growth of the fish population.


During an El Niño event, the trade winds weaken and warm, nutrient-poor water occupies the entire tropical Pacific Ocean. Heavy rains that are tied to the warm water move into the central Pacific Ocean and cause drought in Indonesia and Australia. This also alters the path of the atmospheric jet stream over North and South America.

The effects of El Niño disrupt normal winter conditions throughout the Pacific Ocean, and can persist into May or June. Reliable predictions of an El Niño occurrence will lead to better preparation for its widespread impact.

La Niña

Warm El Niños and cold La Niñas follow each other against the backdrop of the ocean seasons. During a La Niña, the trade winds are stronger and cold, nutrient-rich water occupies much of the tropical Pacific Ocean. Most of the precipication occurs in the western tropical Pacific Ocean, so rain is abundant over Indonesia.