Is it possible to optimise constants of a marine turbulence model by assimilation of observations?

The system of equations describing ocean circulation is statistically avera ged and consequently is not closed. The turbulent diffusive effects need to be parameterised via a turbulence model. Some empirical constants are then necessary to close the system. This work aims to show the feasibility of a pplying the data assimilation method of optimal control to identify these c onstants. A prototypic model with two equations of vertical diffusion for t he velocity and the salinity is considered. The turbulent viscosity and dif fusivity coefficients are computed with a k model. The experiment consists of optimising the two constants of this model by assimilation of velocity a nd salinity data. These observations have at first been numerically constru cted by the simulation of the break of a halocline between two layers, the upper one being in movement. The cost function measuring the discrepancies between the simulation results and the data is minimised iteratively in the direction of its gradient computed by an adjoint model. In spite of the sh ape of the cost function surface with a valley and a plateau, the method co nverges. The difficulties which could be encountered in the parameter optim isation in such non-linear models of marine turbulence, are finally discuss ed. (C) 2000 Academie des sciences / Editions scientifiques et medicales El sevier SAS.