Presenter: Kalyani Manthripragada (NIOT)

Description:
Inclusion of wave induced Stokes drift in the coupled models helps in the accurate estimation of the Langmuir circulation, sediment transport, surface oil or pollutant transport. In this study, the Stokes drift is evaluated from in-situ OMNI buoy observations of NIOT at a location in the central Bay of Bengal (BD11) from long term observations of about 10 years (2011-2021). These are continuous observations of high temporal resolution at three hour intervals. The wave parameters derived from two-dimensional spectra i.e., the bulk wave parameters such as significant wave height, wave periods derived from different spectral moments and the mean wave directions of wind seas, swells as well as combined (total) wave and directional spreading at peak are utilized. Moored buoys generally do not transmit the two-dimensional (frequency-direction) wave spectral information due to data storage limitations. They transmit only the derived statistical parameters, which are the bulk parameters. In this study, the Stokes drift estimates from moored buoy bulk wave parameters are compared with that of ECMWF ERA5 model-spectral as well as model-bulk parameters. The associated model deviations of both spectral and bulk estimates are presented for the same period. The correlation and root mean square error are quantified. Models generally perform well during moderate sea states but deviations are high during severe cyclones where nonlinearities play a significant role. An attempt is made to understand which set of wave statistical parameters best represents the rapidly varying complex mixed (seas & swells) wave climate during different phases of cyclones; associated with different levels of cyclonic influence based on the track distance and changing cyclonic parameters along the track. The seasonal variability of Stokes drift for each year, the inter-annual variability over a decade as well as the peak response and variability during different cyclones will be presented in this study.