Episodes of nonlinear internal waves in the northern East China Sea

Abstract

Episodes of high-frequency internal waves, which lasted approximately 3 hours, were detected in the northern East China Sea during a specific phase of the barotropic tide (i.e., low tide at 32 degrees N, 125 degrees E). The observed internal waves influenced the whole water column. The wave packets were presumably generated near the ocean shelf break, approximately 200 km to the southeast of the test site. During several internal wave episodes, which coincided with the neap tide, large-amplitude solitary wave-like features emerged preceding higher frequency internal waves. Shear instability of tidal currents is explored as a possible mechanism for sustaining or regenerating internal waves in the packets during the course of their propagation. It is suggested that rotating velocity field of tidal current supports sufficient vertical shear within wave packets to cause outbreaks of K-H instability. These instabilities may gradually transition to more symmetric Holmboe waves, following the increase of the bulk Richardson number.