The generation and propagation of internal solitary waves in the South China Sea

The internal wave field in the real-time numerical simulation at the Naval Research Laboratory is analyzed during April-May 2007, a period of intensive field observations in the northern South China Sea. Internal solitary waves are detected in the plots of the surface baroclinic velocity and depth-integrated energy flux. In each diurnal cycle, an internal wave crest with eastward surface velocity arrives at a location west of the Luzon Strait first and is followed by two internal wave troughs of westward surface velocity, in agreement with the arrival of a type-B and then a type-A internal solitary wave described in the literature. Sources of the B-wave and A-wave are consistent with the generation by eastward tidal currents on the western and eastern ridges in the Luzon Strait, respectively. During neap tide, a B-wave and an A-wave switch their daily arrival times to maintain the arrival sequence of an A-wave after a B-wave. Internal waves arriving at a mooring location at the same time each day are B-waves during the neap tide and A-waves during the first half of the spring tide. Otherwise, both A-waves and B-waves have a 1 h delay each day in their daily arrivals. Classification of the internal wave types based on generation gives a coherent pattern of internal wave propagation from the generation region to the continental margin in the South China Sea. The propagation speeds of both waves are higher than that of linear internal waves.