El Nino - and What is the Southern Oscillation Anyway?!

El Nino, an abnormal warming of surface ocean waters in the eastern tropical Pacific, is one part of what's called the Southern Oscillation. The Southern Oscillation is the see-saw pattern of reversing surface air pressure between the eastern and western tropical Pacific; when the surface pressure is high in the eastern tropical Pacific it is low in the western tropical Pacific, and vice-versa. Because the ocean warming and pressure reversals are, for the most part, simultaneous, scientists call this phenomenon the El Nino/Southern Oscillation or ENSO for short. South American fisherman have given this phenomenon the name El Nino, which is Spanish for "The Christ Child," because it comes about the time of the celebration of the birth of the Christ Child-Christmas.
To really understand the effects of an El Nino event, compare the normal conditions of the Pacific region and then see what happens during El Nino below.

Normal C ...more

Source: myself

An El Nio is a temporary change in the climate of the Pacific ocean, in the region around the equator. You can see its effects in both the ocean and atmosphere, generally in Northern Hemisphere winter. Typically, the ocean surface warms up by a few degrees celsius. At the same time, the place where hefty thunderstorms occur on the equator moves eastward. Although those might seem like small differences, it nevertheless can have big effects on the world's climate.