南海西北陆坡次表层异常反气旋涡声传播特征研究

Effects of a subsurface abnormal anticyclonic eddy on sound propagation in the northwest continental slope of the South China Sea

基于2018年4月温盐流断面观测、卫星遥感和模式再分析数据,本文分析了南海西北部陆坡海区一个异常反气旋涡的声场特性与声传播效应。结果表明,该反气旋具有透镜式温盐结构、表层冷核和更浅的混合层深度,流速次表层强化。不同于正常反气旋涡声速等值线的下凹,异常反气旋涡声速分布呈现上凸下凹的透镜式结构。涡心表层声速小于涡外,呈现负异常(<-2 m/s),次表层则为正异常(>11 m/s),这使得原有海区声速双跃层厚度上下延伸共47 m。当声源位于涡外陆架向外海传播时,与正常反气旋涡旋相反,异常反气旋涡破坏表面声道,减小声传播距离;声源在涡外深海向陆架传播时,异常反气旋涡则与正常反气旋涡类似,声能汇聚区的位置相比无涡旋时后移和下移,最大距离分别超过24 km和0.3 km。声源位于涡旋内部向外海传播时,异常反气旋涡使得声线反转深度加深,声能汇聚区间距加大1倍,正常反气旋涡中则未见这一现象。

Using temperature-salinity profiles and current measurements,satellite data and reanalysis data in April 2018,this study analyses the acoustic field characteristics and effects of an abnormal anticyclonic eddy(AAE)on acoustic propagation on the continental slope area in the northwestern South China Sea(SCS).The results show that the AAE has a lens-shaped structure with a surface cold core,a shallower mixed layer,and subsurface intensified velocities.Unlike the concave sound-speed contours in the normal anticyclonic eddy(NAE),the sound-speed distribution in the abnormal anticyclonic eddy(AAE)exhibits a lens-shaped structure with an upward convexity and downward concavity.The surface sound speed within the eddy is lower than that outside,showing a negative anomaly(<−2 m/s).Conversely,the sound speed in the subsurface layer of the eddy is higher than that outside,showing a positive anomaly(>11 m/s).This results in the thickness of the original double thermocline extending up and down by a total of 47 meters in the presence of the eddy.As the sound propagates from the eddy outside on the shelf to the deep sea,the surface sound channel disappears as the propagation distances decreasing in the AAE,contrast to the increased distance in the NAE.As the sound propagates from the eddy outside in the deep ocean to the shelf,the location of the sound energy convergence zone moves backward and downward in the AAE,with the maximum distance exceeding 24 km and 0.3 km,respectively.This is similar to the situation in the NAE.As the sound propagates from the eddy core to outside in the deep sea,the turning depth of the sound deepens and the distance between the sound energy convergence zones doubles in the AAE,while no changes in the NAE.