Bispectra of internal waves in shallow seas

Densely sampled thermistor chain data have been obtained from several shallow‐water acoustics experiments in the Yellow Sea, East China Sea and South China Sea. The data are analyzed to study bispectra of the internal waves observed in this paper. The magnitudes, real and imaginary parts of the bispectra are presented. It is found that strong quadratic interactions occur within the power spectral peak, and also between the peak and its first three harmonics. The real and imaginary parts of the bispectra represent the contributions to the vertical and horizontal asymmetry (skewness and asymmetry) of the internal wave elevations from each frequency pair, respectively. The nonzero asymmetry values indicate the sawtoothlike waveforms. Bispectral analysis is thus a useful means for investigating nonlinear properties of shallow‐water internal waves. [Work supported by NSFC.]