Sea breeze case study using a combination of observations and numerical simulation in complex terrain in Southern France: contribution to matter transport.

Sea breeze dynamics in the Marseille area, in southern France, is investigated in the framework of the ESCOMPTE experiment conducted during summer 2001 in order to evaluate the role of thermal circulations on pollutant transport and ventilation. The complex terrain of the target area (mountainous area with two major valleys), the synoptic situations and the coastline shape are so many parameters that can impact on the three dimensional structure and dynamics of the sea breeze flow. The 25 june 2001 case is studied using a combination of instrumental data from meteorological surface stations, Doppler lidars and sodar and a numerical simulation that was completed using the mesoscale french non-hydrostatic model Méso-NH.

This study reveals that three major processes contribute to the transport of matter: the advection of pollutants inland is mainly driven by two breeze cells that occur on two different depth and time scales, and vertical exchanges between the atmopsheric boundary layer and the free troposhere can be generated at the breeze front and near the slopes due to the development of anabatic winds. The horizontal and vertical mass fluxes are quantitatively evaluated thanks to the numerical simulation.