The monsoon reversal winds in different seasons and high influx of freshwater from various rivers make the Bay of Bengal (BoB) a unique region. Thus, the knowledge of the dynamics of the mixed layer over this region is very important to assess the climatic variation of the Indian subcontinent. A comprehensive study of the role of external forcing on the seasonal and interannual mixed layer depth (MLD) variability over the BoB is carried out for 36 years (1980–2015) using reanalysis products. A weak and strong seasonality of MLD is observed over the northern and the southern BoB (NBoB and SBoB) respectively. The partial correlation suggests that the net heat flux (Qnet) is the major contributor to the deepening of MLD over the NBoB, whereas the wind stress controls the deepening over the SBoB. The seasonal variability reveals the deepening of MLD during summer and winter monsoon and the shallowing during pre- and post-monsoon over the BoB. The relation of the interannual MLD variability and the different phases of the Indian Ocean Dipole (IOD) reveals that the negative phase of IOD is associated with deeper MLD over BoB while the positive phase of IOD depicts shallower MLD. In addition, the opposing characteristic of MLD is highly prominent during October-December. This is majorly contributed by variations related to the second downwelling Kelvin and associated Rossby waves over BoB for the opposing phases of the IOD years.

不同季节的季风逆风以及来自不同河流的大量淡水涌入，使孟加拉湾（BoB）成为一个独特的地区。因此，了解该地区混合层动力学的知识对于评估印度次大陆的气候变化非常重要。使用重新分析产品对外强迫在BoB上的季节性和年际混合层深度（MLD）变异性中的作用进行了长达36年（1980-2015年）的综合研究。在北部和南部BoB（NBoB和SBoB）分别观察到MLD的季节性较弱和较强。偏相关表明，净热通量（Qnet）是NBOB上MLD加深的主要因素，而风应力控制了SBoB上的加深。季节变化揭示了在夏季和冬季季风中MLD的加深，以及在BoB上季风前后的MLD的变浅。MLD的年际变化与印度洋偶极子（IOD）不同相位的关系表明，IOD的负相位与BoB上的更深的MLD有关，而IOD的正相位表示更浅的MLD。此外，MLD的相反特征在10月至12月期间非常突出。这主要是由于在IOD年的相反阶段，第二个向下的Kelvin波和与BoB相关的Rossby波相关的变化所致。MLD的年际变化与印度洋偶极子（IOD）不同相位的关系表明，IOD的负相位与BoB上的更深的MLD有关，而IOD的正相位表示更浅的MLD。此外，MLD的相反特征在10月至12月期间非常突出。这主要是由于在IOD年的相反阶段，第二个向下的Kelvin波和与BoB相关的Rossby波相关的变化所致。年际MLD变异性与印度洋偶极子（IOD）不同相位的关系表明，IOD的负相位与较BoB更深的MLD有关，而IOD的正相位则表示较浅的MLD。此外，MLD的相反特征在10月至12月期间非常突出。这主要是由于在IOD年的相反阶段，第二个向下波的Kelvin波和BoB上的相关Rossby波的变化所致。