孟加拉湾上层地转环流周年变化的遥感研究

应用1993～2003年TOPEX/Poseidon卫星测高数据结合历史水文资料,反演了孟加拉湾海面动力地形的平均周年变化,探讨了孟加拉湾上层环流季节特征和演变规律.结果显示,虽然孟加拉湾的大气环流受季风支配年周期波动显著,但表层环流形态的周年演变却呈3个不同的阶段.1～4月间(东北季风后期)湾内受一个海盆尺度的强大反气旋式环流的支配,湾口为西向流;5月西南季风骤起,印度季风漂流越过印度半岛南端出现在湾口,湾内反气旋环流弱化,在其南北两侧各出现一气旋式涡,构成5～9月间南北相间的三涡结构;10月东北季风再起,湾口漂流再次转向,10～12月间湾内则为海盆尺度的弱气旋式环流.受上述环流格局影响,位于西边界的印度沿岸流亦呈相应的3个阶段变化.分析表明,孟加拉湾风应力旋度的变化是造成湾内环流3个阶段演变的主要原因.本地风场和来自赤道海域的外强迫的共同驱动形成了孟加拉湾环流周年演变的独特规律.

Annual variation of geostrophic circulation in the Bay of Bengal observed with TOPEX/Poseidon altimeter data

TOPEX/Poseidon satellite altimetry data from 1993 to 2003,combined with histroical hydrographic data,is used to reproduce climatological monthly surface dynamic topography in the Bay of Bengal (BOB).The characters and rules of seasonal evolution of the upper circulation in the BOB are then discussed.Analyses indicate that although dominated by the seasonal reversing Indian monsoon,yet annual variation of the BOB surface circulation could be divided into three stages with distinctive patterns.During Jan through April (the late northeasterly monsoon),the BOB circulation is maily controlled by a basinscale strong anticy clonic gyre with a westward current (Indian monsoon current,IMC) developing in the Bay mouth.From May,responsing on southewestly monsoon abrupt onset,IMC reverses,passing throuth south tip of Indian peninsula,and then intrudes into the bay.In the interior bay,the anticyclonic gyredecays,with two cyclonic gyres prevailing in north and south side of it respectively,forming three-eddy structure during May through September.With northeasterly monsoon onset in October,IMC in the Bay mouth reverses again.The interior Bay is dominated by a basin-scale weak cyclonic circulation during October) December.Affected by annual variation of the BOB circulation,the western boundary current in the BOB also indicates corresponding three-stage variation.It is suggested that three-stagevariation of the BOB circulation is mainly driven by wind stress curlin the interior.Both local wind and equatorial remote wind contribute to annual evolution of the BOB circulation.