EVERYDAY SCIENCE

Detailed explanation-1: -During an El Niño event, westward-blowing trade winds weaken along the Equator. These changes in air pressure and wind speed cause warm surface water to move eastward along the Equator, from the western Pacific to the coast of northern South America.

Detailed explanation-2: -During normal conditions in the Pacific ocean, trade winds blow west along the equator, taking warm water from South America towards Asia. To replace that warm water, cold water rises from the depths-a process called upwelling.

Detailed explanation-3: -As the warm ocean surface warms the atmosphere above it, moisture-rich air rises and develops into rain clouds. So while the majority of precipitation tends to occur over the west Pacific warm pool in neutral years, much more develops over the central and eastern Pacific during an El Niño event.

Detailed explanation-4: -During El Niño, the surface winds across the entire tropical Pacific are weaker than usual. Ocean temperatures in the central and eastern tropical Pacific Ocean are warmer than average, and rainfall is below average over Indonesia and above average over the central or eastern Pacific.

Detailed explanation-5: -During El Niño (bottom panel of diagram to the left), the trade winds relax in the central and western Pacific leading to a movement to the east of the warm pool of water. This warm pool of water moves eastward until it spreads across the entire Pacific Ocean.