热带东印度洋表层环流季节变化特征研究

Seasonal variation of surface-layer circulation in the eastern tropical Indian Ocean

利用近20 年的卫星遥感海面绝对动力高度（Absolute Dynamic Topography, ADT）数据、表层流数据及Argos 表面漂流浮标数据等研究了热带东印度洋表层环流的季节变化特征.分析结果显示, 热带东印度洋表层环流的变化与季风演替基本同步, 赤道以北海域环流季节变化特征甚为显著.与此大尺度环流年循环同步, 孟加拉湾湾口环流也相应变化： 湾口东部在5~9 月为南向流, 一直延伸至苏门答腊岛外海, 其他月份, 从湾口东部至整个苏门答腊岛外海（4°S 以北）为北向流; 湾口西部经向流的变化大体与东部相反.Argos 漂流浮标轨迹进一步揭示了湾内外各季节水交换路径： 西南季风期, 源自阿拉伯海及印度半岛南部海域的漂流浮标主要通过西南季风漂流由湾口西侧进入湾内, 湾内的漂流浮标通过湾口东侧沿着苏门答腊岛进入赤道印度洋; 东北季风期, 漂流浮标进出湾口的途径大体与西南季风期相反.本研究还表明, 季风海流及赤道急流的纬向流速季节变化最大, 而经向流速的季节方差最大的则为东印度沿岸流及拉克沙群岛高压（拉克沙群岛低压）.关键字： 热带东印度洋; 孟加拉湾; 表层环流;

Seasonal variation of the surface-layer circulation in the eastern tropical Indian Ocean （ETIO） is analyzed using nearly 20years of surface absolute dynamic topography （ADT） data derived from satellite observations, ocean surface currentanalysis-realtime （OSCAR） data and the trajectories of Argos surface drifters. The results show that the seasonal variations of thesurface circulation and the monsoons in the ETIO are almost coinstantaneous. The seasonal variations are more significant north ofthe equator. With this seasonal cycle of large-scale circulation, the circulation at the mouth of the Bay of Bengal changesaccordingly. During May-September, the eastern mouth of the bay is dominated by the southward meridional current, which extendsfurther southward off Sumatra, while it reverses to flow northward during the rest months. The meridional current in the western baymouth is generally opposite to that in the east. The Argos drifting buoy trajectories further reveal that the water exchange pathwaysin and out the bay change seasonally. During the summer monsoon, the drifting buoys from the southern India Ocean and theArabian Sea are mainly drifted into the bay from the west side of the bay mouth, while those from the bay are drifted out from theeast side. The pathway reverses during the winter monsoon. This study also shows that the maximum variance of the zonal currentsis caused by the monsoon currents including the Wyrtki Jet, while the maximum variance of the meridional currents is due to theEast Indian Coastal Current （EICC） and Lakshadweep High （Lakshadweep Low）.