An Observational Study of the Local and Remote Response of the Equatorial Pacific to Westerly Wind Events during the 1991-92 El Nino
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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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 Navys 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 temperature SST up to 1 deg C. These 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 deg C in the central and eastern equatorial Pacific. These fluctuations propagated eastward at phase speeds consistent with first baroclinic equatoriaL Kelvin wave dynamics i.e., 2.0 - 3.5 Ms--. The ocean temperature fluctuations indicate basin wide wavelengths about 15 x 103 km, with periods of 30-60 days.
- Atmospheric Physics