Low-level-jet-induced pumping in the atmopsheric boundary layer in the lee of the Alps during a north foehn event

Pumping of aerosol and moisture, from the atmospheric boundary layer (ABL) into the free troposphere, has been observed over the Po valley during a north foehn event documented in the framework of the Mesoscale Alpine Programme Special Observing Period (MAP SOP). Airborne lidar (i.e. atmospheric reflectivity at 732 nm and water vapor mixing ratio) observations in the lower troposphere suggest that the pumping is related to the presence of low-level jets (at 1500 m above sea level) in the lee of the Alps. The pumping was observed to be most outstanding in the vicinity of the city of Milano, Italy. High resolution numerical simulations down to 2-km using Meso-NH have been used to investigate this process.