吕宋海峡黑潮西侧3个气旋涡的三维结构与演变特征

THREE-DIMENSIONAL STRUCTURE AND EVOLUTION OF THREE CYCLONIC EDDIES TO THE WEST OF THE KUROSHIO IN THE LUZON STRAIT

黑潮入侵南海会诱生中尺度涡,对南海与西太平洋物质能量交换起着重要作用。前人对黑潮诱生反气旋涡研究较多,而对气旋涡研究较少,对其三维结构和生消过程也不清楚。利用卫星高度计数据和再分析数据,选取2018~2019年间南海东北部的3个气旋涡(cycloniceddy,CE)CE1、CE2和CE3,研究了其三维结构与演变特征,并初步讨论了其生成机制。研究结果表明:3个气旋涡生成于吕宋海峡西南部黑潮主轴左侧,半径约为47~87km,生成后都向西移动,最长距离可达255km,远小于该区域中尺度涡平均移动距离。气旋涡的最大旋转速度约为0.4~0.6m/s,垂向深度可达1 200~1 600 m。3个气旋涡中心水体上涌,温度异常均为负值,在垂向上呈单核结构,冷核的位置在50~600m处,冷异常最大可达-2°C;中心盐度异常垂向上呈现“正-负-正”的三核结构,分别位于0~100 m、200~400 m和500 m以下深度,低盐异常最大可达-0.26。黑潮锋面的正压不稳定性是气旋涡生成的主要因素,能量从黑潮动能向涡动能转移,是气旋涡生成所需能量的主要来源。

The Kuroshio intrusion into the South China Sea(SCS)can induce mesoscale eddies,which play an important role in the exchange of matter and energy between the SCS and Western Pacific Ocean.Previous studies focus on anticyclonic eddies induced by Kuroshio and eddy shedding processes.However,cyclonic eddies are less investigated,their three-dimensional structure and evolution remain unclear.Three cyclonic eddies(CE1,CE2,and CE3)in the northeastern SCS formed during 2018~2019 were selected.By using satellite altimeter data and reanalysis data,three-dimensional structure and evolution characteristics of the eddies were studied,and their forming mechanism was discussed.Results show that:cyclonic eddies were generated in the southwest of the Kuroshio in the Luzon Strait,their mean radius were between 47~87 km.They all moved westward in the maximum distance of 255 km,which was far less than the average moving distance of regional mesoscale eddies.The cyclonic eddies rotated counterclockwise in the maximum velocity of 0.4~0.6 m/s,and the vertical depth extended to 1200~1600 m.The water in the centers of the cyclonic eddies were uplifted,and the temperature in eddy center showed a negative anomaly with a single core in vertical direction.The cold core was located at 50~600 m,and the maximum cold anomaly reached-2°C.The central salinity anomaly presented a vertical three-core structure of“positive-negative-positive”located at 0~100 m,200~400 m,and below 500 m in depth,respectively,and the lowest salinity anomaly reached-0.26.The barotropic instability of the Kuroshio front was the controlling factor on the generation of the cyclonic eddies.