On the impact of ocean/wave coupling in tropical cyclones conditions in the Indian Ocean

Ocean waves play a key role in the exchange of heat and momentum fluxes between the ocean and atmosphere, expecially in extreme wind conditions. The availability of directional wave spectra from SWIM lead to a better description of wave systems nearby the trajectories of tropical cyclones as shown recently by Le Merle et al. 2022. Also the assimilation of these directional observations induced an improved forecast of integrated wave parameters and initial conditions from wind-sea to swell propagation. The objective of this work is to examine the impact of the wave-ocean coupling under cyclonic conditions in the Indian Ocean. Coupled simulations between the MFWAM wave model and the NEMO ocean model have performed over the 2020 and 2021 cyclonic seasons in indian ocean. We used an improved wave forcing by assimilating the directional wave spectra and the corresponding significant wave heights provided by the instrument SWIM of CFOSAT satellite. The impact of this enhanced wave forcing on the ocean circulation was compared with the one without CFOSAT data assimilation. The main coupling processes are wave-modified stress, Stokes drift and wave breaking induced turbulence. The results show that wave/ocean coupling leads to a significant increase of the ocean mixed layer along the trajectories of cyclones. This clearly induces a cooling of the upper ocean layers at the rear of the cyclones. The validation of key ocean parameters indicates an improvement in sea surface temperature compared to satellite data (OSTIA). We investigated the currents variability in the upper ocean following the trajectory of cyclone HEROLD. We also examined the impact of the coupling process driven by the wave breaking induced turbulence and investigated a better parametrization than the used one from Craig and Banner (1992). Further conclusions and comments will be discussed in the final presentation of this work.