Study of the stratification of the urban boundary layer of Marseille under sea-breeze condition

3D numerical simulations, with the Meso-NH atmospheric model including the Town Energy Balance urban parameterization, are conducted over the south-east of France and the one million inhabitants city of Marseille in the frameworks of the ESCOMPTE-UBL program. A complete evaluation of the model was already realized at both regional- and city-scales, by using the large available database. This present work focuses on the 250-m horizontal resolution outputs to specifically study the fine vertical structure of the Urban Boundary Layer (UBL) over Marseille during the 26 June 2001 (i.e. the last day of IOP 2b), which is characterized by a south flow and a weak pressure gradient favoring the development of thermal circulations. With this aim, the numerical results are compared to the data of the transportable wind lidar (TWL). Located at Vallon Dol in the north of Marseille, it documented the flow circulations over the city by providing radial velocity measurements along the line-of-sight. In the direction of Marseille, the data cover an area of 6 km across the city and 3 km according to the altitude, with a radial range resolution of about 300 m. This original evaluation shows the coherence between the stratification of the atmosphere underscored by the lidar measurements and the one modeled by Meso-NH at a similar resolution. This is followed by an analysis of the backtrajectories of the model in order to study the origin of the air masses, which converge over the city and produce such a complex UBL.