Statistical representation of equatorial waves and tropical instability waves in the Pacific Ocean

Sea surface height (SSH), sea surface temperature (SST), and surface currents derived from satellite observations are analyzed to investigate signals of equatorial Kelvin and tropical instability waves (TIWs) in the Pacific Ocean. A wavenumber–frequency spectral analysis of SSH and SST anomalies was performed in order to examine their space and time variability. Significant spectral peaks along the dispersion curves of the first baroclinic mode Rossby and Kelvin waves are found in the SSH spectrum, indicating that the analysis can effectively identify the signals of equatorial waves in the upper ocean. A prominent peak in SSH fields at around 33 days and 1500 km wavelength along the Rossby wave dispersion curve is evident, and a similar peak is also found in SST fields. This upper ocean variability on these space and time scales is shown to be associated with TIWs. The spatial structure of 33-day TIWs is further examined based on an analysis of time series filtered in the frequency-wavenumber domain. The phase relationship between SSH, SST, and surface velocity associated with TIWs is described based on a cross-correlation analysis. Also, the interannual variability of TIW activity is compared with that of ENSO, showing a moderate correlation.