Research On The Mechanism Of Internal Solitary Waves Generated By The Resonance Of The Same-scale Terrain And Background Current

This paper uses the mooring data set in the west of Dongsha Islands of the northern South China Sea,combined with the topographic data of the area,to statistically analyze the characteristics of the internal solitary waves in this area,and carried a numerical experiment of internal solitary waves with different wavelength and model.The velocity and propagation speed characteristics of internal solitary waves generated by the resonance mechanism of terrain and background current are analyzed.During the mooring observation,the period of internal waves in this area is mostly between 20-30 minutes.The amplitude of internal waves is most in the 20-40 meters,followed by the40-60 meters.Both the maximum amplitude and maximum period of the internal waves appeared in autumn,the maximum amplitude was close to 100 m which appeared in September and the maximum period was 69 min,which appeared in November.In summer and autumn,there are more internal waves and the amplitude of internal waves is larger seasons.During the observation,the maximum of current velocity is appears with internal solitary waves,indicating that the internal solitary wave will significantly increase observation current.The background velocity before the internal waves is mainly southwest,and is small,especially in the middle and bottom layers,and the velocity does not exceed 40 cm/s.When internal waves occur,the observed velocity is affected by internal waves.The upper flow velocity changes from southwest to west,and the rate of flow velocity greater than 50cm/s is as high as 34.44%.current at the middle layer begins to turn east,and at the bottom layer,the flow velocity direction is generally opposite to that in the upper layer,which is southeastward(21.14%)or eastward(14.86%),and the velocity is slightly lower than upper layer.The four-wavelength of first-mode internal solitary waves are all concave internal solitary waves,and their propagation speed is relatively close to the maximum amplitude.The horizontal velocity is all northwestward in the upper layer and southeast in the lower layer.With regard to the vertical velocity,the vertical structure of the waves with the wavelength of 4.3km,3.3km and 2.4km is more obvious,and the upwelling after the wave peak with the wavelength of 6.6km is not obvious.The vertical structure simulated by the resonance mechanism is consistent with the vertical structure of the background buoyancy frequency,and is basically consistent with the vertical profile structure of the observed zonal velocity.The position where the maximum zonal velocity appears is basically consistent with the observation,with differences of 5m,0m,12 m and 15 m respectively.The vertical section of the calculated velocity of the solitary wave in the second mode is different from the background buoyancy frequency structure.It has two inflection points and has the characteristics of the second mode internal solitary waves.It has a certain similarity with the observed velocity,and the maximum value of the velocity appears close to it.However,the velocity change at a depth of 65 m is not as fast as the velocity observed,and its characteristics are not reflected.Whether first mode internal solitary wave or the second mode internal solitary wave,the propagation speed of the internal solitary wave calculated by the resonance mechanism is relatively small,which is 0.13m/s-0.45m/s smaller than the propagation speed calculated by the Kd V equation.Numerical experiment results show that the resonance mechanism of terrain and background current can characterize some internal solitary waves in the sea area on the west side of the Dongsha Islands of the northern South China Sea,especially the first mode internal solitary waves in,but the result of the second mode is not accurate.