Simulations of Internal Solitary Wave Interactions with Mesoscale Eddies in the Northeastern South China Sea

Abstract

ith the combined analysis of synthetic aperture radar image and satellite altimeter data collected in the northeastern South China Sea (SCS), this study found one type of distorted phenomenon of internal solitary wave (ISW) with the long front caused by the oceanic mesoscale eddy. Motivated by these satellite observations, the authors carried out numerical experiments using the fully nonhydrostatic and nonlinear MITgcm to investigate the perturbation of ISWs by an isolated cyclonic or anticyclonic eddy. The results show that the ISW front is distorted by these oceanic eddies due to the retardation and acceleration effects at their two sides. The ISW energy along the front is focused onto (scattered from) the wave fragment where a concave (convex) pattern is formed, and the previously accumulated energy in the focusing region is gradually released after the ISW propagates away from the eddies. The ISW amplitude is modulated greatly by the eddies due to the energy redistribution along the front. Sensitivity results indicate that the magnitude of the modulated ISW amplitude in the focusing region can reach twice the incident ISW amplitude, while in the scattering region it can be reduced by more than a half. These results therefore suggest that models with eddies included, especially the energetic eddies, could further improve the amplitude predictions in the northeastern SCS. Additionally, the internal gravity wave formed behind the energy-focusing region by the anticyclonic eddies can steepen and break with the consequent formation of a secondary trailing ISW packet. Finally, this study shows that the model results of the distorted front and trailing packet are in qualitative agreement with that of the satellite observations in the northeastern SCS.