GEOSAT Altimeter Observations of Kelvin Waves and the 1986-87 El Nino.

Two years of GEOSAT altimeter observations are used to investigate the response of sea level to anomalous westerly wind bursts in the tropical Pacific Ocean before and during the 1986-87 El Niño. Sea level time series along the equator show examples of both positive and negative anomalies of 10-centimeter amplitude and 2- to 4-week time scale propagating across the Pacific with phase speeds of 2.4 to 2.8 meters per second, suggesting downwelling and upwelling Kelvin waves, respectively. A comparison of island wind observations with sea level indicates one instance (May 1986) in which a positive sea level anomaly can be related to westerly winds caused by a cross-equatorial cyclone pair in the western Pacific. This episode was followed by additional wind bursts later in the year, and finally by sustained westerlies in the western Pacific during November-December 1986, at the height of El Niño. The GEOSAT observations reveal the sea level response to these meteorological events and provide a synoptic description of the El Niño oceanographic phenomenon.