The El Niņo/Southern Oscillation (ENSO) is a natural climate cycle that occurs irregularly over several years. A pool of very warm surface waters shifts from one end of the tropical Pacific Ocean to the other, accompanied by a tremendous center of tropical rainfall. The shifting oceanic and atmospheric circulation dramatically rearranges wind and rainfall patterns over more than half the globe. In fact, ENSO is second only to the seasons themselves in driving worldwide weather patterns.
La Niņa is another extreme phase of the climate oscillation known as ENSO (short for El Niņo Southern Oscillation). In this phase, the central equatorial Pacific becomes much colder than normal.