Abstract's details

On the improvement of ocean/wave coupling with CFOSAT directional wave observations

Lotfi Aouf (Division Marine et Océanographie Météo-France, France)


Stéphane Law-Chune (MOI, France); Danièle Hauser (LATMOS/CNRS, France); Bertrand Chapron (IFREMER, France); Cedric Tourain (CNES, France)

Event: 2022 Ocean Surface Topography Science Team Meeting

Session: CFOSAT

Presentation type: Type Keynote/invited

The propagation of waves at the air-sea interface strongly influences surface stress and turbulent mixing in the upper ocean layers. Better estimate of directional properties of sea state should improve the turbulent mixing that deepens the ocean surface boundary layer. The CFOSAT mission provides directional wave spectra that can better scale wind-wave growth and the transition to swell regime. This induces a significant improvement of integrated sea state parameters (Aouf et al. 2021). The objective of this work is on the one hand to assess the impact of wave directionality on ocean circulation, and on the other hand to analyze the dominant wave/ocean coupling term in critical ocean areas where there is high uncertainty on wind forcing such as Southern Ocean and the tropics. To this end several coupled global simulations between the MFWAM wave model and the ocean model NEMO have been implemented globally with a grid resolution of 25 km. The wave model is used with and without assimilation of directional wave spectra and off-nadir wave heights of CFOSAT (SWIM beam 10°). The experiments were carried out over the periods from January to April for the years 2020 and 2021. Firstly, the validation of Significant Wave Height (SWH) from the MFWAM model with independent altimeters data shows significant reduction in bias and scatter index when the assimilation of CFOSAT observations is activated. We have selected the ocean regions where the impact of assimilation is strongest and we examined the impact on ocean wave forcing represented by surface stress, Stokes drift and wave breaking inducing turbulence in the ocean mixed layer. We validated key ocean parameters (current, temperature, elevation, salinity) with in situ observations and satellite data. The results show a significant improvement in surface currents in the Southern Ocean, particularly in the vicinity of the Antarctic Circumpolar Current. We also found an improvement of the surface current in the tropics. Analysis on the oceanic mixing layer indicates a significant impact of the waves. This results in an improvement in the surface temperature in the southern ocean, particularly in the Weddell Sea and between southern Australia and the Antarctic.
Further comments and conclusions will be addressed in the final presentation.

Keynote/invited presentation show times:

Room Start Date End Date
Sala Pasinetti Thu, Nov 03 2022,10:15 Thu, Nov 03 2022,10:30
Lotfi Aouf
Division Marine et Océanographie Météo-France