Observations of nonlinear internal waves over the shelf break of the East China Sea

Abstract

First- and second-mode nonlinear internal waves (NIWs) were observed over the shelf break of the East China Sea in July 2017 and 2018, respectively, with nearly full depth measurements of velocity and temperature. In addition to a wave train propagating northwestward, perpendicular to isobaths of the continental slope, wave trains propagating westward and even southwestward were observed as well. The propagation speeds of first- and second-mode NIWs were about 1.2 and 0.34 ms-1, respectively, regardless of the direction of propagation. Each wave train arrived at an interval of about one day, suggesting that these NIWs were generated by the diurnal tide. Measurements of the dissipation rate of turbulent kineticenergy and energetic analysis indicate that the first-mode NIWs are able to propagate over the entire continental shelf of the East China Sea before dissipating. In fact, downward displacements of isothermal surfaces associated with the first-mode NIWs (about 10-20 m) were nearly the same as those previously observed in the northern continental shelf of the East China Sea in summer.