Performance of ERA5 winds on computed storm surge and wave-current interaction using a coupled model during Ockhi cyclone

Abstract

A fully coupled numerical model was setup to simulate tides as well as storm surges and waves generated by the very severe cyclonic storm Ockhi, which occurred in the Arabian Sea during 29 November-6 December 2017. ERA5 hourly wind data as well as cyclonic winds generated from a parametric wind model were used separately as input to assess the accuracy of these winds in generating waves during cyclones. Both the data produced reasonably accurate maximum surge heights, with an underestimation of ? 0.2 m in the model surge height from one another. The results showed that model forced with ERA5 winds could reproduce the cyclone-generated waves to better accuracy than the waves generated by the parametric model winds. With ERA5 winds, coupled model generated Hs ? 1.12 m and the standalone model generated Hs ? 1.44 m. Results showed that due to wave-current interaction, Hs reduced by 0.32 m. The modelled waves showed an underestimation of 1-2 m during cyclone peak in the deep waters, whereas it matches closely with the measurements in the coastal region. It was also observed that during the cyclone, the NE monsoon enhanced the ebbing flow and reduced the flooding, which caused change in the current flow direction at the time of landfall.