LAUSR

Abstract The calculation of the meridional overturning streamfunction in the southern Indian Ocean is biased by the Indonesian Throughflow. Therefore, this study applies the vertical overturning streamfunction to diagnose the shallow overturning circulation in the Indian Ocean. Using the Ocean General Circulation Model for the Earth simulator output, improvements with the vertical overturning streamfunction compared with the meridional overturning streamfunction are explored. The results show that the vertical overturning streamfunction smoothly connects the shallow overturning circulations of the northern Indian Ocean and the southern Indian Ocean with the whole cycle of the subtropical cell and the cross-equatorial cell. The vertical overturning streamfunction shows a much cleaner shallow overturning circulation, which is underestimated by the meridional overturning streamfunction. It shows that the shallow overturning circulation has a magnitude of ~13 Sv (1 Sv 106 m3 s−1), of which the subtropical cell accounts for ~8 Sv. In addition, the vertical overturning streamfunction captures a clockwise overturning cell in the upper 600 m layer between 30°S and 34°S. This cell has a magnitude of about −5 Sv and probably corresponds to the wind-forced subtropical gyre. Therefore, the vertical overturning streamfunction provides a new approach for estimating the shallow overturning circulation in the Indian Ocean. 摘要 由于印尼贯穿流干扰了南印度洋经向翻转环流的计算, 本文应用垂向翻转流函数来诊断印度洋浅层经向翻转环流. 基于海洋环流模拟产品 (OFES), 本文探讨了垂向流函数相比经向翻转流函数的改进. 研究结果表明垂向翻转流函数能平滑连接南北印度洋的翻转环流, 包括完整的副热带翻转环流和跨赤道翻转环流. 经向翻转流函数低估了印度洋浅层翻转环流; 而垂向翻转流函数表示的印度洋浅层翻转环流受印尼贯穿流影响更小, 其评估的印度洋浅层翻转环流强度约13 Sv, 其中副热带翻转环流强度约8 Sv (1 Sv 106 m3 s−1). 此外, 垂向翻转流函数在印度洋南开边界 (30°S~34°S) 上600 m层表现为顺时针翻转结构, 其强度约−5 Sv, 可能对应风驱的副热带流系. 因此, 垂向翻转流函数提供了一种新方法来评估印度洋浅层翻转环流.