An Observational Study Of Long Waves In The Equatorial Pacific Ocean During The 1991 1993 El Nino

Long waves in the equatorial Pacific Ocean during the 1991-1993 El Nino event were examined using temperature, current, and wind time series from the Tropical Oceans-Global Atmosphere Tropical Atmosphere-Ocean (TOGA-TAO) moored buoy array. Numerous episodes of long wave activity were detected. The most prominent episodes were associated with eastward propagating equatorial Kelvin waves and with westward propagating tropical instability waves and mixed Rossby-gravity waves. Equatorial Kelvin waves, which were generated by westerly wind events in the western and central Pacific, were evident in the data between 2 deg N to 5 deg S and from 170 deg W to 110 deg W. These Kelvin waves, which were most pronounced from 75 to 300 m, had periods of 40 to 70 days, eastward phase speeds of 1.9 to 6.5 m/s, and zonal wavelengths on the order of 10,000 km. These waves were most evident in the northern hemisphere fall and winter. The period of greatest Kelvin wave activity was August 1991 -May 1992, during the peak phase of the 1991-1993 El Nino event.