(El Niño -Southern Oscillation) is a composite term referring to the whole suite of events associated with these negative SOI episodes.
El Niño – Southern Oscillation El Niño Southern Oscillation Climatic phenomenon occurring in the Tropics that involves transports of warm (El Niño) or cold (La Niña) water masses from west to east across the Pacific basin. This displacement of water is accompanied by a shift of atmospheric cells, and therefore of winds and monsoons across the Tropics. This oscillation, which has been occurring at irregular intervals for thousands of years, has a global effect on climate. The phenomenon is named "El Niño" (meaning the Christ Child or the Little Boy in Spanish) because warm waters often reach the coast of Peru around Christmas time, often severely disrupting local fisheries.
a suite of events that occur at the time of an El Niño; at one extreme of the cycle, when the central Pacific Ocean is warm and the atmospheric pressure over Australia is relatively high, the ENSO causes drought conditions over eastern Australia ( see El Niño, SOI)