Spatiotemporal variations of parameters of internal solitary waves in the northern South China Sea

The dynamic parameters for internal solitary waves (ISWs) derived from the extended Korteweg-de Vries (eKdV) equation play an important role in the understanding and prediction of ISWs. The spatiotemporal variations of the dynamic parameters of the ISWs in the northern South China Sea (SCS) were studied based on the reanalysis of long-term temperature and salinity datasets. The results for spectrum analysis show that there are definite geographical differences for the periodic variation of the parameters: in shallow water, all parameters vary with a wave period of one year, while in deep water wave components of the parameters at other frequencies exist. Using wavelet analysis, the wavelet power spectral densities in deep water exhibited an inter-annual variation pattern. For example, the wave component of the dispersion coefficient with a wave period of about half a year reached its power peak once every two years. Based on previous work, this inter-annual variation pattern was deduced to be caused by dynamic processes. In further work on the regulatory mechanisms, empirical orthogonal function (EOF) decomposition was performed. It was found that the modes of the dispersion coefficient have different geographical distributions, explaining the reason why the wave components in different frequencies appeared in different locations. The numerical simulation results confirm that the variations in the parameters of the ISWs derived from the eKdV equation could affect the waveforms significantly because of changes in the polarity of the ISWs. Therefore, the periodic variations of the dynamic parameters are related to the geographical location because of dynamic processes operating.