Simulation of El Niño of 1982–1983

A general circulation model of the ocean simulates El Niño of 1982–1983 with reasonable success and provides the following results. The massive eastward transfer of warm surface waters from the western to the eastern Pacific was accomplished by unusual eastward surface currents which, by November 1982, extended from 9°S to 9°N across 120°W. Further east, the persistence of the southeast trades over the eastern tropical Pacific inhibited eastward surface flow at, and to the south of the equator at that time, but the eastward flow between 3° and 8°N penetrated right to the coast of Central America. The relaxation of the trades and the changes in the curl of the windstress, that caused the redistribution of heat in the upper ocean, occurred so gradually between June and November 1982 that the response of the ocean was approximately an equilibrium one. The zonal pressure gradient along the equator and the intensity of the Equatorial Undercurrent, for example, decreased gradually as the trade winds weakened. In December 1982, the anomalous eastward winds west of the dateline suddenly changed to northerly winds. The westward pressure force which the eastward winds had established was left unbalanced. This excited an eastward travelling equatorial Kelvin wave which elevated the thermocline and accelerated the equatorial currents westward. The wave front dispersed downwards as it propagated eastward and there is no evidence of its reflection at the South American coast affecting the surface layers of the ocean. Eastward winds in the eastern equatorial Pacific Ocean in March and April interrupted the recovery from El Niño and generated an intense local eastward surface jet. The reappearance of the tradewinds in May 1983 signalled the end of El Niño and the gradual return to normal conditions.