Numerical Investigation Of The Internal Solitary Wave In The Northeastern South China Sea Based On Nonhydrostatic Model

The nonhydrostatic ocean model SUNTANS is firstly improved with respect tothe calculatin method of the horizontal eddy viscosity and the mesh parameters, whichmakes the numerical stability and adaptability of the model improved. The modifiedmodel is then employed to investigate the generation, propagation and evolution ofthe internal solitary wave in the northeasten South China Sea. The main results aresummarized as follows:Based on the theoretical results and in-situ observation data, the influence of fourclassic flux limiters of the TVD scheme, which are used to solve the equations oftemperature and salinity, on the numerical results is analyzed. It is demonstated thatthe results with the MUSCL limiter are the best among these with the four limiters. So,the MUSCL limiter is suggested to be used for the simulation of the internal solitarywave in the northeasten South China Sea.According to the simulated results of the three dimensional nonhydrostatic model,the internal solitary wave observed on the continental slope and shelf mainlyoriginates from the depression wave generated by the interaction of barotropic tidalcurrent with the ridges in the Luzon Strait. The initial depression wave disintegratesinto internal solitary waves by nonlinear steeping during its propagation. The largera-waves align close to the peak eastward barothopic tidal current at the ridge, and thesmaller b-waves align close to the maximamm westward current.The three dimensional simulation results can reasonably depict the refraction anddiffraction of the internal solitary wave propagating on the continental slope and shelf.In the deep basin, the a-wave travels faster than the b-wave mainly because of theirlarger amplitudes. The propagation speed of the b-wave is larger than that of thea-wave on the continental slope, which is due to the modulation of the diurnal internaltide from the Luzon Strait.The generation of the second mode internal solitary waves, which have beenrecently observed many times, is numerically investigated. The second mode internalsolitary wave is found near the shelf break in the simulated results, and the positon isconsistent with the results of remote sensing image. The simulated results indicate thatthe generation of the second mode internal solitary wave is related to the interactionof the first mode internal solitary wave with the topography near the shelf break. The influence of the seasonal variation of the stratification on the generation andpropagation of internal solitary waves is numerically investigated. It is revealed thatthe seasonal variation of the amplitude and propagation speed is due to the change ofthe stratification. The thermocline in the upper layer plays a significant role in thegeneration of internal solitary waves. The internal solitary wave can also be generatedwith deeper mixed layer and thermocline. The generation of internal solitary waves issuppressed when the thermocline in the upper layer disappears. The weakening ordisappearance of the thermocline in the upper layer is the possible reason for the lowoccurrence frequencies of internal solitary waves in the winter.The algorithm of parallel computing with one and multiple GPUs for thenonhydrostatic model is developed. The calculated results show that the speedup ofGPU parallel computing scheme increases when the number of grid cells or theinvolved GPU increases, and the speedup can increase quasi-linearly with respect tothe number of GPUs for the problem with more grid cells, demonstrating wellscalability of the scheme.25.4times speedup is achieved with four GPUs for the casewith120×104three dimensional grid cells.