Mistral and tramontane simulations with changing resolution of orography

Abstract

Mistral and tramontane are mesoscale winds in southern France. Both winds emerge in valleys and cause deep water formation in the Mediterranean Sea, which makes them interesting phenomena for studying several orographic effects and relevant for Earth system models. However, climate simulations are performed on a finite numerical grid with a coarse-gridded orography and processes on subgrid scales are parameterized. This study surveys the effect of orographic grid spacing (2.6–45 km) on mistral and tramontane by performing idealized simulations with a 1.3 km horizontal numerical grid. Reduction of the orographic detail leads to a wind pattern change and a wind speed reduction. If orographic features on smaller scales are parameterized, the effects of the smoothing are weaker, but a systematic decrease in channeling and wind speed still persists.