Sensitivity of the northwestern Mediterranean Sea coastal and thermohaline circulations simulated by the 1/12°-resolution ocean model NEMO-MED12 to the spatial and temporal resolution of atmospheric forcing

The northwestern Mediterranean (NWM) Sea is prone to intense weather events, associated with high winds, that are characterized by strong shallow jets and a high spatial and temporal variability. The ocean response in this area is very sensitive to the atmospheric conditions, particularly in the Gulf of Lions coastal zone.The ocean response to strong winds is here investigated using the NEMO-MED12 eddy-resolving model, driven by four atmospheric forcings differing in spatial resolution (20 km, 6.7 km) and temporal resolution (daily or 3 h) and produced with the non-hydrostratic mesoscale WRF model.The noticeable effects of the higher-frequency forcing are (i) to reduce the shelf dense-water formation and the deep offshore convection in winter due to the explicit simulation of the diurnal cycle that warms and stratifies the ocean upper layers and (ii) to increase the vertical velocity in the upwelling cells. The higher spatial resolution allows, in particular, the production of stronger winds and the accurate reproduction of the near-surface sub-mesoscale eddies in the coastal areas, in agreement with observations.

► We examine coastal processes with the regional NEMO-MED12 model.
► We use four atmospheric forcings differing in space and/or time resolution.
► The higher frequency reduces the deep convection and the dense water formation.
► The finer space resolution increases the vertical velocity in the upwelling cells.