Lateral Boundary Conditions at the staircase-like boundary of ocean models

National audienceA 4D-Var data assimilation technique is applied to a rectangular-box configuration of the NEMO in order to analyze the optimal parametrization of boun\-dary conditions at lateral boundaries. The impact of staircase-shaped coastlines is studied by rotating the model grid around the center of the box. Rotations on $30^\circ$ and $45^\circ$ are studied with single and double gyre forcing patterns. It is shown that optimized boundary conditions compensate the errors induced by the staircase-like approximation of the coastline