Séminaire : Michel Tchilibou (LEGOS): Spectral signatures of the tropical Pacific dynamics from model and\naltimetry: A focus on the meso/submesoscale range
Tuesday 13 March 2018, 11:00am - 12:00pm
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Abstract : The processes that could contribute to the flat Sea Surface Height (SSH)
wavenumber spectral slopes observed in the tropics by satellite altimetry are examined in the tropical Pacific.Based on a 1/12° global model, the tropical dynamics is investigated from spectral analysis to discuss on anisotropic signature, ageostrophic motions, kinetic energy flux with a special focus on the meso/submesoscale range. The equatorial region is dominated at every scales by anisotropic and ageostrophic motions. The spectral signature of kinetic energy is dominated by the Tropical Instability Waves with a peak of energy at 1000 km, an inverse cascade of energy for scales larger than 500 km, and an inertial like forward cascade down from 500 km. The off-equatorial regions are characterized by a relatively narrow 100-250 km mesoscale range dominated by an inverse cascade of energy. Both regions have modeled surface power KE spectra consistent with 2D QG and SQG turbulence that do not explain the observed altimetric spectra. Sea level does not respond to the ageostrophic equatorial dynamics, and the wavenumber SSH wavenumber spectra have low spectral power but maintain a steep slope consistent with quasi-geostropic turbulence. Based on 1/36° high-frequency regional simulations, with and without explicit tides, we find a strong signature of internal waves and internal tides in the western tropical Pacific that act to increase the smaller-scale SSH spectral energy power and flattening the SSH wavenumber spectra, in accordance with the altimetric spectra. Coherent M2 baroclinic tide is the dominant signal at ~ 140 km wavelength, but the shortest scales are dominated by incoherent internal tides which extend up to 200 km in wavelength, therefore impacting on alongtrack altimetric SSH today and on the future SWOT swath observations raising the question of SWOT observability at short scales in the

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Location salle de réunion LOCEAN, tour 45/55, 4eme étage

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