An observational study of the local and remote response of the equatorial Pacific to westerly wind events during the 1991-92 El Nino

Abstract

The upper equatorial Pacific Ocean response to anomalous westerly wind forcing during the 1991-92 El Nino was examined using observed oceanographic and atmospheric data from equatorial moorings and the Navy's operational atmospheric analyses. A strong 30-60 day signal was observed in the zonal winds and is mainly a result of westerly wind events. The local response to anomalous westerly winds differed between the western and eastern equatorial Pacific. In the western Pacific, westerly wind events tended to produce rapid decreases in sea surface temperatures (SST) (up to 1 degree C). There decreases were followed several days later by SST increases due to horizontal warm water advection and downwelling. In the central and eastern equatorial Pacific, westerly wind events were expressed mainly as weakenings of the easterlies. These weakenings caused decreases in equatorial upwelling and SST increases Westerly wind events in the western Pacific were also associated with large thermocline temperature fluctuations (on the order of 10 degrees C) in the central and eastern equatorial Pacific. These fluctuations propagated eastward at phase speeds consistent with first baroclinic equatorial Kelvic wave dynamics (i.s., 2.0 - 3.5 ms-1). The ocean temperature fluctuations indicate wide wavelengths (about 15 X 10(3)km), with periods of 30-60 days.