Near‐Inertial Waves and Their Underlying Mechanisms Based on the South China Sea Internal Wave Experiment (2010–2011)

Abstract

AbstractBased on mooring array data from the South China Sea (SCS) Internal Wave Experiment, in this paper, five burst events of near‐inertial waves (NIWs) in the northern SCS that occurred during August 2010 to April 2011 are reported. Among these NIWs, three were induced by typhoons Lionrock, Meranti, and Megi in 2010. Due to the differences in typhoon characteristics, mooring measuring ranges, distances between typhoon centers and moorings, and local conditions, the NIWs induced by the three typhoons show various intensities and structures at all three moorings. An interesting phenomenon is that the weaker typhoon Meranti generates stronger NIWs than the stronger typhoon Megi, which is largely due to the larger translation speed of Meranti. The e‐folding time of near‐inertial variance suggests that the damping of typhoon‐induced NIWs is related to local conditions. In addition to the typhoon‐induced NIWs, two NIW burst events were found in December 2010 and March 2011 at one mooring; however, these events were absent from the two adjacent moorings. Through analysis, we ruled out the local winds, lateral propagation, and parametric subharmonic instability as the causes of these NIWs. Although the real mechanisms remain unknown, the NIWs that occurred in December 2010 and March 2011 exhibit different features from the typhoon‐induced NIWs. First, these NIWs have larger vertical wave numbers and smaller wavelengths than the typhoon‐induced NIWs. Second, these NIWs can cause intense shear in deep water, whereas intense shear of typhoon‐induced NIWs mainly exist in the upper ocean (approximately 150–200 m).