孟加拉湾中尺度涡的总体特征与季节变化

采用AVISO提供的中尺度涡最新数据集,分析了孟加拉湾1993—2016年中尺度涡的总体特征和季节变化。结果表明:研究期间在孟加拉湾共有822个气旋涡,731个反气旋涡,主要分布在湾北部(15°N以北海域)和安达曼海。涡旋生命周期以28～59 d为主,平均振幅为7. 5 cm,平均半径为119. 6 km。在纬度变化上,涡旋振幅随纬度的增加有两个峰值,分别位于6°～9°N和15°～20°N之间,而涡旋半径随纬度增加而减少。涡旋的振幅、半径在随生命周期演变过程中生长过程较慢,消散过程较快。气旋涡和反气旋涡主要是向西移动,且均以向赤道方向偏移为主。在季节变化上,孟加拉湾较长生命周期(60 d以上)的中尺度涡具有明显的季节变化,春季生成的涡旋数量最多,冬季次之,夏季最少。通过合成分析得出风应力旋度是孟加拉湾中尺度涡季节变化的主要原因,而沿岸Kelvin波激发的西传Rossby波对涡旋的产生也有一定影响。涡动能分析表明,涡动能的高值区主要位于海盆的西边界和斯里兰卡东部海域,同时,在冬季、春季海盆的西边界和夏季、秋季海盆的北部涡旋活动较多的区域对应着较大的涡动能。

General features and seasonal variation of mesoscale eddies in the Bay of Bengal

The general features and seasonal variation of mesoscale eddies in the Bay of Bengal from 1993 to 2016 are analyzed based on the latest data set of mesoscale eddies provided by AVISO. The result shows that there are 822 cyclones and 731 anticyclones in the Bay of Bengal, and they mostly distribute in the north of 15°N in the Bay of Bengal and the Andaman Sea. Eddy lifetimes are mainly ranged from 28 to 59 days. Cyclones and anticyclones have an average amplitude and radius of 7.5 cm and 119.6 km, respectively. The amplitude has two peaks in 6°-9°N and 15°-20°N and the average radius of eddies gradually decreases with increasing latitude. The amplitude and radius of the eddy grows slowly and dissipates fast during the evolution of eddy. Cyclones and anticyclones mainly move to westward and tend to move toward the equator. The mesoscale eddies with a longer lifetime (more than 60 days) have an obviously seasonal variation in the Bay of Bengal, and the eddies are mostly generated in spring, the next in winter and the less in summer. The synthetic analysis concludes that the wind stress curl is an important reason for the seasonal variation of the mesoscale eddies and the westward propagating Rossby wave radiated by coastal Kelvin wave has a certain influence on the generation of mesoscale eddy in the Bay of Bengal. The analysis of eddy kinetic energy indicates that the high value zone of eddy kinetic energy is mainly located in the western boundary of the basin and in the east of Sri Lanka, while the region with strong eddy activity corresponds well with the larger eddy kinetic energy in winter and spring in the western boundary of the basin and in summer and autumn in the north of the basin.