Observations and modelling of wind seas and swells in the Bay of Bengal

The spatial and temporal evolution of wind seas and swells during the monsoon seasons were examined as a part of the U.S. (Office of Naval Research and Naval Research Laboratory) sponsored programs in collaboration with India and Sri Lanka, Monsoon Intra-Seasonal Oscillations in the Bay of Bengal (MISOBOB) from July 2018 to June 2019. Directional wave spectral data were collected from upward-looking 300 kHz acoustic Doppler current profilers (ADCPs) with wave packages at five moorings in the Bay of Bengal (BoB). The ADCPs were mounted at 60 to 90 m below the surface. Four moorings were deployed at 8° N, 10° N, 12° N, and 14°N along 85.75° E, and the fifth mooring was deployed in the region encompassing the Sri Lanka Dome (~83.75° E, 8° N). Wave observations were compared with model results from the WAVEWATCH III (WW3) ocean wave model that produced hourly directional wave spectra for the entire BoB at 0.25° resolution. Analyses of directional wave spectra from both observations and model simulations show significant differences in their evolution between summer and winter monsoon seasons. Fortuitously, Cyclone FANI passed over the northern moorings (12° N and 14° N) from April 30 to May 2, 2019. During the passage of the cyclone, the significant-wave height reached 7.6 m with a peak period of 12 s at 14° N. Directional wave spectra simulated by the WW3 during the cyclone are evaluated by comparing against observations.