Data assimilation method by a variational methodology using the adjoint ofa 3-D coastal circulation primitive equation model.

The optimal control technique using an adjoint method is applied to fit the parameters of a 3-D primitive equation coastal model due to a data assimil ation procedure. Two of the main unknowns of coastal modelling operations - open boundary conditions and turbulent mixing processes in stratified cond itions - are successively considered. The aim of the boundary control proce dure is to identify boundary forcing to ensure the best fit between data an d model results by minimising a function that measures model and data discr epancies. A methodology for proceeding from the continuous to the discrete formulation of a control problem is given. The robustness of the method is tested for the typical barotropic case of a semi-enclosed basin Kelvin wave . The data assimilation method of optimal control is then applied to the tu rbulence closure problem in the framing of coastal oceanic circulation. Num erical simulation of a schematic destruction of an halocline and an upwelli ng event resulting from a wind stress imposed at the sea surface in a stron gly stratified two-layer case are realized. The adjoint method is used to f ind out an optimal set of viscosity and diffusivity coefficients which perm its the retrieval of the closest computed simulation to hydrodynamic synthe tic observations. (C) 2001 Ifremer/CNRS/IRD/Editions scientifiques et medic ales Elsevier SAS.