Lateral diffusion in terrain-following coordinates: a challenge

Authors: Patrick Marchesiello and Xavier Couvelard
Affiliation: IRD, Noumea center

We have applied the nested version of ROMS (ROMS_AGRIF) to the southwest Pacific. The region has complexe topographic features including numerous islands, ridges and trenches. These are generally meridionally orientated, i.e. accross the dominant zonal flow. A terrain-following coordinate model is therefore a proper tool to investigate the role of topography in shaping the South Equatorial Current and driving its multiple branches. However, we have found along the way that the model solution is very sensitive to the choice of lateral diffusion, provided either through diffusive advection terms or diffusion operators. We will argue that, after recent advances have been made in the pressure gradient computation, the problem of lateral diffusion in terrain-following coordinates might present a new challenge.