This paper investigates experimentally, numerically and theoretically the mechanism of wake formation. It shows that the flow impinging on the Alpine range and the Massif Central transition to supercritical all along the ridge line, including the Rhône valley and continue to accelerate in the lee regions until a hydraulic jump occurs. This leads to the formation of strong wakes behing and close to the peaks.
Wake formation in the lee of the Alps and the Massif Central causes large inhomogeneity of the planetary boundary layer. In the region of the wakes, enhanced convection associated to larger surface sensible heat fluxes is observed and simulated leading to deeper planetary boundary layer. In the Mistral jet, cold air advection inhibits the planetary boundary layer development.