Numerical Simulation of the Interannual Variability of the Bay of Bengal Ocean Circulation Characteristics by Regional Ocean Modeling System (ROMS)

The interannual variations of the Bay of Bengal (BoB) ocean circulation features have been investigated with the Regional Ocean Modeling System (ROMS) for the period of 2004-2014. The ROMS simulations for the BoB have been extended from 4°N to 24°N and 76°E to 100°E. We use a horizontal resolution of 9 km with 32 terrain-following vertical levels for these model runs. The initial condition is derived from the Mercator Ocean global data for 1st January, 2004 and the boundary conditions are derived from the daily Mercator data for the period 2004-2014. The model is forced with the 3 hourly forcing from the ECMWF Air-Sea fluxes and with the monthly river discharges. The interannual simulations are carried out with and without river input to estimate the relative importance of local and remote forcing. We discuss the model performance and analyze the trends and variability of temperature, salinity and water mass over the basin for the period of 2004-2014. We also present the year-to-year changes in the occurrence, movement and lifecycle of the mesoscale and submesoscale eddies, and their influences on the strength of boundary currents in the western BoB during the IOD and ENSO years. The simulations reveal that variations in wind stress can induce significant interannual changes in the circulation of the upper layers. The interannual response is more pronounced in the western BoB with the boundary currents Western Boundary Current (WBC) towards north and East India Coastal Current (EICC) towards south in this region. It is found that the influence of Indian Ocean Dipole (IOD) is more prominent than El Niño Southern Oscillation (ENSO) on the interannual variability in the BoB. The interannual changes of upwelling and downwelling signals become stronger during ENSO and IOD years in the western BoB.