Orographic Precipitation in the Alps

Due to the availability of long-term rain gauge observations, the European Alps are particularly well suited to investigate the spatial distribution, longterm trends, and underlying dynamical and microphysical processes of orographic precipitation events. Heavy events are a common phenomenon in the Alps, and mean annual precipitation maxima exceed 100 mm/day at many locations. The Alps have been the target area of a major field campaign -- the Mesoscale Alpine Program (MAP) -- which took place in the autumn 1999. Particular consideration was given to the (sometimes devastating) heavy precipitation events that frequently occur on the southern slopes of the Alps. Bob Houze has been one of the key scientists behind setting up, conducting and exploiting this field experiment. His group’s research led to a number of discoveries, relating to the dynamics and microphysics of orographic precipitation. Some of his research flights made an early attempt to exploit high-resolution convection-resolving NWP models for real-time mission planning. Among other factors, he investigated aspects of the large-scale moist flow past the Alpine barrier, the role of upslope precipitation, embedded convection, microphysical processes, as well as the relevance of turbulence and synoptic-scale disturbances. Overall a coherent picture of dynamically-driven orographic precipitation events in the Alps emerged. In this presentation, an overview of some of this research will be provided.