Neap-spring variability of internal waves over the shelf-slope along western Bay of Bengal associated with local stratification

Interaction of barotropic tide with the continental shelf break region is studied in the presence of local stratification. To achieve this, MITgcm is developed for the western part of Bay of Bengal to simulate the internal tide that manifests itself as internal wave (IW) of predominant M-2 tidal frequency. The QuikSCAT daily winds and real-time tides along with monthly climatology of density are used as initial forcing fields to drive the model. From the energy spectra analysis, variability of dominant semi-diurnal IWs is addressed on both spatial and temporal scales. Computed spectral estimates of temperature and density fields off Visakhapatnam using the time series data are in good agreement with observations during 23-25 February 2007 and 18-20 October 2006. Isopycnal displacement of about 15 m is computed which compared well with observations for February 2007, confirming the presence of internal tides. Spectral energy peak is higher for spring than for neap as the associated astronomical forcing is maximum. The IW peak is simulated at 75 m depth which falls within the pycnocline depth. Two vertical cross sections bearing different stratifications along the Bay of Bengal coast are studied to delineate IW energy propagation over the shelf-slope region. The spatial model results show that the location of peak energy shifted a few kilometres onto the shelf towards the coast during October. Our simulation results during February and October demonstrate that IW energy varies across the shelf break with energy peaks at the shelf break, and their dissipation range is affected by the degree of stratification.