Day 4

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Paper title On the joint use of wide swath Significant wave height and directional wave spectra for global wave forecasting
Authors
  1. Lotfi Aouf Meteo France, CNRM Speaker
  2. Danièle Hauser CNRS, Université Saint Quentin en Yvelines, Paris Sorbonne Université
  3. Jiuke Wang NMEFC
  4. Bertrand Chapron Ifremer - LOPS
  5. Cédric Tourain CNES
Form of presentation Poster
Topics
  • A8. Ocean
    • A8.14 Remote-sensing of Ocean Waves and their Applications
Abstract text One of the challenge of future earth system for climate prediction, is to better understand the exchange of momentum, heat and gas fluxes at air-sea interface. In this context, the waves play a key role for the estimate of accurate forcing terms to the upper ocean layers and feedback to the atmosphere. Currently the global wave system of the Copernicus Marine Service (CMEMS) is jointly assimilating Significant Wave Height (SWH) from altimeters and directional wave observations from CFOSAT and Sentinel-1. This leads to significant improvement of integrated wave parameters of sea state, particularly in ocean regions affected by strong uncertainties related to the wind forcing, for instance the Southern Ocean. Among the promising recent developments, we can highlight the synergy between waves and wind observations as provided by CFOSAT mission, which has shown the capacity of retrieving wide swath SWH with good accuracy (Wang et al. 2021). This work gives an overview of using both wide swath SWH and directional wave spectra from satellite missions (CFOSAT, Sentinel-1, HY-2B, HY-2C) in operational wave model. We show that the performance of such assimilation system induces a significant reduction of normalised scatter index of SWH, which is in average smaller than 8%.
We investigated the impact of using both directional wave spectra and wide swath SWH in critical ocean regions suh as the southern ocean and the tropics, with particular attention to consequences on ocean circulation. We also draw up the improvement induced by the assimilation of directional wave spectra on the wind-wave growth and the estimate of wave group speed under unlimited fetch conditions. In this work we examined the complementary use of wave spectra from wave scatterometter SWIM and SAR for better capturing swell propagation. In other respects the persistency of the assimilation of wide swath SWH and directional wave spectra is extended to 4 days in the forecast period, which ensures good reliability for wave submersion warning and marine security bulletins.
Further results concerning the impact of wave directionality on upper ocean mixing has been investigated in the tropics and in the area of Antarctic Circumpolar Current (ACC) ocea area. figure illustrates the zonal mean of eastward component of the current between 146°-149°E of longitudes in Southern ocean from NEMO model simulations and observations from drifters (AOML products). This clearly reveals the improvement of the surface currents when ocean model is coupled with improved wave forcing which uses directional wave spectra and swath SWH.
More discussions and conclusions will be summarized in the final presentation.