International audienceA 4D-Var data assimilation technique is applied to the rectangular-box configuration of the NEMO in order to identify the optimal parametrization of boundary conditions on lateral boundaries. The case of the staircase shaped coastlines is studied by rotating the model grid around the center of the box. It is shown that, in some cases, the formulation of the boundary conditions on the exact boundary leads to appearance of exponentially growing modes while optimal boundary conditions allow to correct the influence of the stair-case-like boundaries
