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The ocean plays a major role in climate change, and its impact has an extreme effect on the process of coastal and other activities around the globe. The comprehensive analysis of long-term wave climate is carried out at selected locations in the western Bay of Bengal (BoB), by observing the distribution of significant wave height (SWH) using monthly averaged satellite and WAM model for 20 years (1996–2015). The data used in this study were compared with two in situ buoy observations obtained from the National Institute of Ocean Technology (NIOT), Chennai, India. The satellite and wave model (WAM) data show a good correlation with both in situ buoy observations. The probability distribution functions indicated a significant increase in the higher range of SWH during the recent decade. The analysis of 20-year SWH indicates a positive trend with significant annual and semiannual periodicities. The northwestern bay depicts higher energy in the annual cycle, whereas the southwestern bay exhibits equal contributions from annual and semiannual cycles. The study also reveals that the increasing trends in local SWH in the western BOB are modified due to the number of tropical cyclones as well as the migrating swells generated in the southern Indian Ocean.

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.