Qn. Zheng et al., OBSERVATION OF EQUATORIALLY TRAPPED WAVES IN THE PACIFIC USING GEOSATALTIMETER DATA, Deep-sea research. Part 1. Oceanographic research papers, 42(5), 1995, pp. 797-817
A spatial integration filtering method is applied to process 4.5 years
of Geosat altimeter sea level anomalies (SLA) recorded from 1 April 1
985 to 17 September 1989. The integral limits are chosen as +/- 1.5 de
grees latitude centered at the equator and +/- 4 degrees longitude cen
tered at the each central longitude. These limits are chosen in order
to eliminate the random noise and to enhance the equatorially trapped
wave signals. The spatial-integration-filtered SLA time series show pe
riodical signals with different time scales. Processing the SLA time s
eries with a Short Time Fourier Transform (STFT) yields the lime-frequ
ency spectra of the SLA which show a frequency spectral splitting-comb
ining phenomenon in the periods during and after the 1986-1987 El Nino
-Southern Oscillation (ENSO) event. Analysis of non-linear wave-wave i
nteraction indicates that this phenomenon results from amplitude modul
ation of the short period oscillations in the 60-100 day band by a lon
g period oscillation with a period of about 500 days. The wave compone
nts of the short period oscillations are further analysed using the eq
uatorial wave modes to fit the meridional distribution of the SLA. The
results indicate that the downwelling Kelvin wave mode before and dur
ing the peak phase of 1986-1987 ENSO and the upwelling Kelvin wave mod
e during the 1988 La Nina are the dominant components. The first and s
econd Rossby wave modes play important roles for entire time series an
d occasionally become the dominant components. The mean phase speed of
Kelvin wave mode during the 1986-1987 ENSO is 3.0 m s(-1), which is 2
5% higher than those in non-ENSO periods.