Remote sensing evidence for baroclinic tide origin of internal solitary waves in the northeastern South China Sea

TLDR

The study proposes that internal solitary waves in the northeastern South China Sea arise from nonlinear steepening of baroclinic tides generated by strong tidal currents over the Luzon Strait ridge, rather than from lee‑wave processes. The authors classify ISW packets into single‑wave and multiple‑wave types and attribute their formation to nonlinear steepening of baroclinic tides over the Luzon Strait ridge. Satellite observations of 116 internal wave packets (including 22 single‑wave packets in deep water) from 1995 to 2001, corroborated by an ERS‑2 SAR image, support the baroclinic tide origin hypothesis.

Abstract

Evidence for baroclinic tide origin of internal solitary waves (ISWs) in the northeastern South China Sea is presented, based on 116 internal wave packets observed in satellite images from 1995 to 2001. These wave packets can be divided into two types, a single‐wave ISW packet containing only one ISW with/without an oscillating tail, and a multiple‐wave ISW packet composed of a group of rank‐ordered ISWs. All of the 22 single‐wave ISW packets occur in the deep water zone. It is suggested that the ISWs, instead of being generated by the lee‐wave mechanism, are developed by nonlinear steepening of the baroclinic tides, which are produced by the strong tidal currents flowing over a ridge in Luzon Strait. This suggestion is verified by an ERS‐2 SAR image, which records such an evolution process from a baroclinic tide to a single ISW in its spatial domain.