Energy And Volume Transport By Internal Solitary Waves In Northern South China Sea

Internal solitary waves is one of the important dynamic processes in the ocean, due to its strong velocity, large amplitude and great influence sphere, ISWs should carry tremendous energy, horizontal and vertical volume transport during propagation from west of Luzon Strait, through the deep basin and onto the continental shelf. But due to the limit of depth and time range of observation in SCS is rare, the full-depth characteristic parameters, energy, energy flux, volume transport of ISWs and their time variation are unknown. The characteristic parameters, energy, energy flux, volume transport of ISWs are calculated, and their time variation are analyzed.ISWs are present 7.5% of the time at 2000 m depth in the deep basin of SCS. ISWs are weaker in the winter because of the deep surface mixed layer and weaker stratification. And ISWs are least frequent in the winter,0.67 num per day, and most frequent in the summer,1.28 num/day. The maximum along-wave velocity exceeds 2 m/s, it is 0.89 m/s on average. The maximum amplitude is as large as 187 m, and it is 95 m on the average. The propagation direction vary mainly from 270°N to 300°N and is 283°N on average, ISWs propagate westward.The time variation of energy is analyzed, the energy and energy flux of ISWs is larger in the summer and weaker in the winter. The kinetic energy and available potential energy are roughly equal, the energy of ISWs at mooring position is o(1 GJ/m). Energy flux includes velocity-pressure work term and nonlinear advection of energy, neutral regression indicates uE=0.1444up, the annual mean energy flux is-7.72 KW/m, velocity-pressure work term and nonlinear advection of energy is -6.73 KW/m and -0.99 KW/m, respectively.For the volume transportation of ISWs, it is larger in summer and autumn, and least in winter. The continuous horizontal transportation of particle by ISWs is as far as 40 km. The annual mean volume transport was -4.62 m3/s in the upper layer and 6.04 m3/s in the lower layer. It was the same order with mesoscale eddies because of the high frequency and intensity of ISW in SCS. The asymmetry of ISWs caused net heat transport which was mainly downward. The depth averaged heat flux of one ISW was as high as o(105 W/m2). The annual mean depth averaged J was downward 2.05 KW/m2, which was one order more than the averaged background turbulent diffusivity in northern SCS.