Observed Three-dimensional Structure of Internal Solitary Waves in the Northern South China Sea

Yunchao Yang1, Xiaodong Huang2, Wei Zhao1 and Jiwei Tian3, (1)Ocean University of China, Qingdao, China, (2)Ocean University of China, China, (3)Ocean university of China, Qingdao, China
A cross-shaped array, consisting of 10 moorings deployed from Oct 2013 to Jun 2014, is used to investigate the three-dimensional structure of internal solitary wave (ISW) and its temporal variations in the deep basin of northern South China Sea (SCS). Measurements reveal that ISW in the northern SCS is asymmetric along crest, characterized by the stronger south portion than north portion on average. The strongest part of ISW is generally located at 20°15′N, where the maximum orbital velocity is 20% faster than that at the crest-center mooring at 20°50′N. Ray-tracing result suggests that the stronger (weaker) south (north) portion of ISW mainly originates from the ridges south (north) of Batan Island in the Luzon Strait. Moreover, modulated by mesoscale eddies and Kuroshio, the three-dimensional structure of ISW exhibits dramatic temporal variations, and the wave crest patterns are interconverted among three types: convex, concave and S-shaped, accounting for 76.2%, 4.2% and 19.6%, respectively. Due to the along-crest energy redistribution by those background processes, wave properties vary out of phase between the north and south potions of crest, and 13.5% ISWs shift their along-crest strongest part from the south portion to north portion. The time-averaged energy and energy flux of ISW in the deep basin calculated based on the three-dimensional wave structure are 49 TJ and 0.75 GW, respectively.