| Ocean internal wave is an important dynamic process and has important effects on the energy cascade,mass transport,and acoustic processes in the ocean.The northern South China Sea is a high-incidence area of internal solitary waves,most of which originate from the interaction between astronomical tides and the topography of the Luzon Strait.This paper studies the internal solitary waves in the northern South China Sea from different angles,including the generation of internal solitary waves in the Luzon Strait,the westward propagation in the deep sea basin,the wave-wave interaction near Dongsha Island,and extracting characteristic parameters of internal solitary waves from SAR(Synthetic Aperture Radar)remote sensing data,etc.First,based on multi-source SAR remote sensing images,the temporal and spatial distribution characteristics of the solitary wave crest line crossing phenomenon near Dongsha Island are revealed.The results show that there are wave crossing phenomena on the west,northwest,south and north sides of Dongsha Island,but concentrated on the northwest side,and the crossing frequency in summer is more than other seasons;combined with the parameterization method,the internal solitary wave characteristic parameters near Dongsha Island are rretrieved,and the obtained amplitude is between 21-38 m,which is not that consistent with the measured data;for the retrieving of the amplitude in shallow water,based on the physical theory of the parameterization method,an empirical correction factor related to the water depth and the characteristic half-width of the internal solitary wave is proposed and verified.The result shows the corrected amplitude result is closer to historical measured data.Secondly,combined with SAR satellite remote sensing data and previous research results,an in-depth numerical study was conducted on the generation mechanism,propagation characteristics and influence factors of the two special types of internal solitary waves – a-and b-waves in the northern South China Sea: through comparison between the results of control run and sensitivity experiments of topography,it is found that the source of a-wave is located in the south-central part of the east ridge of the Luzon Strait,while the source of b-wave is located in the northern part of the Luzon Strait and is likely to be located on the west ridge.At the same time,from an energy point of view,we find the combined effect of the ridge topography on the astronomical tide provides a part of the energy when the a-wave is generated,and also creates the necessary conditions for the b-wave.By comparing the results of control run and sensitivity experiment of the tidal component,it is found that the semidiurnal tide is dominant in the generation of a-and b-waves,and the diurnal tidal component affects the generation time and amplitude of the a-and b-waves.At the same time,it is also found that the tidal cycles changes of the semidiurnal and diurnal tide on the spring and neap tide is a reason for the phenomenon of "switching" during the large and small tides.Finally,combined with the SAR satellite remote sensing data,numerical models and the wave-wave interaction theory of internal solitary waves,in view of the typical internal solitary wave crossing phenomenon shown in a SAR image on the south side of Dongsha Island,the wave-wave interaction phenomenon near Dongsha Island has been systematically explored,and the whole process of the time-space change of the wave-wave interaction has been tracked using a numerical model.The numerical model results show that the amplitude of the internal solitary wave is consistent with the amplitude retrieved from the SAR image;the wave-wave interaction type of the internal solitary wave changes from the [2143] type to the [3142] type during the propagation process.Considering that the numerical model adopts the real bottom topography of variable water depth,by calculating the changes of the relevant parameters in the wavewave interaction theory during the entire wave-wave interaction process,it is found that this changing of the type is caused by the changes in water depth,but the evolution of the wave-crossing part of the wave-wave interaction can also be supported by the extended Miles theory. |
