Contribution de Lucile GAULTIER, Jacques VERRON, Pierre BRASSEUR & Jean-Michel BRANKART:

On the inversion of high resolution tracer image for the control of ocean circulations emerging from altimetric data

During the past 20 years, altimetric satellites have revealed the turbulent ocean dynamics at the mesoscale. Additionally, high resolution sensors of tracers such as the Sea Surface Temperature or the Ocean Color reveal even smaller structures at the submesoscale, which are not detected by altimetry. Therefore, the two types of complementary observations are expected to refine the estimation of the ocean circulation. The goal of this study is to explore the feasibility of inverting tracer information to possibly control ocean dynamics emerging from altimeter data analysis. To do so, we choose an image data assimilation strategy in which a cost-function is built that aims at minimizing the misfits between some image of submesoscale flow structure and tracer images. In the present work, we have explored the extent to which the Finite-Size Lyapunov Exponents (FSLE) can be considered as a proxy characterizing the submesoscale flow structure. A prerequisite to the study is the investigation of the sensitivity of FSLE horizontal patterns to velocity errors. Indeed, the misfit between a FSLE derived from a velocity with errors, and the FSLE derived from an error free velocity is successfully minimized. The next step is the inversion of tracer information using real data. The ocean dynamical variable to be corrected is the mesoscale altimetric velocity (from AVISO) using a high resolution tracer image (from MODIS). The cost function measures the misfit between the FSLE derived from the altimetric velocity and the high resolution tracer image. Several test cases have been studied and show the feasibility of the inversion of tracer information to correct altimetric data. The error made on the solution of the inversion process is further investigated using a model.

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