Different Types of Near-Inertial Internal Waves Observed by Lander in the Intermediate-Deep Layers of the South China Sea and Their Generation Mechanisms

Abstract

We report the direct and quantitative measurement of five significant near-inertial waves (NIWs) events observed by Lander at water depths of 600 m to 1100 m at 119°17′ E and 22°06′ N in the northern South China Sea from July to November 2017. We found that these five NIWs events lead to strong shearing, which plays an important role in deep water mixing. Each event corresponds to several different NIWs generation mechanisms. The results show that the NIWs events generated by typhoons were the most regular. This was caused by dispersive NIWs propagation over long periods of time and over long distances. NIWs formed by spontaneous generation do not have this feature. The strongest NIWs events during the observation period were caused by a combination of shelf wave attenuation and monsoon. This time, the signal was transmitted to the seabed, and the upward signal reflected in the meridional direction was found. The reflected signal was anisotropically affected by the seabed topography. A horizontally propagated NIWs event with relatively weak dispersion was also found in this study. Based on the topography, we suspect it was formed by the Lee wave, but we cannot provide any more useful evidence.