Effects of high-order nonlinearity and rotation on the fission of internal solitary waves in the South China Sea

A variable coefficient, rotation-modified extended Kortweg-deVries (vReKdV) model is applied to the study of the South China Sea (SCS), with focus on the effects of the high-order (cubic) nonlinearity and the rotation on the disintegration process of large-amplitude (170 m) Internal Solitary Waves (ISWs) and the semi-diurnal internal tide propagating from the deep basin station to the slope and shelf regions in a continuously stratified system. The numerical solutions show that the high-order nonlinearity significantly affects the wave profile by increasing the wave amplitude and the phase speed in the simulated area. It is shown that the initial KdV-type ISW will decay faster when the rotation dispersion is considered, however the wave profile does not change significantly and the rotation effect is not important. The simulations of the semi-diurnal internal tide indicate that the phase of the wave profile is shifted earlier when the rotation effect is included. A solitary wave packet emerges on the shelf, and the wave speed is also greater when considering the rotation dispersion. In addition, the effects of the background currents are discussed further in this paper. It is found that the background currents generally change the magnitude and occasionally change the sign of the nonlinear coefficients in the northern SCS.