Föhn in the Rhine Valley during MAP: A review of its multiscale dynamics in complex valley geometry

This paper summarizes the findings of seven years of research on fohn conducted within the project 'Fohn in the Rhine Valley during MAP' (FORM) of the Mesoscale Alpine Programme (MAP). It starts with a brief historical review of fohn research in the Alps, reaching back to the middle of the 19th century. Afterwards, it provides an overview of the experimental and numerical challenges identified before the MAP field experiment and summarizes the key findings made during MAP in observation, simulation and theory. We specifically address the role of the upstream and cross-Alpine flow structure on fohn at a local scale and the processes driving fohn propagation in the Rhine Valley. The crucial importance of interactions between the fohn and cold-air pools frequently filling the lower Rhine Valley is highlighted. In addition, the dynamics of a low-level flow splitting occurring at a valley bifurcation between the Rhine Valley and the Seez Valley are examined. The advances in numerical modelling and forecasting of fohn events in the Rhine Valley are also underlined. Finally, we discuss the main differences between fohn dynamics in the Rhine Valley area and in the Wipp/Inn Valley region and point out some open research questions needing further investigation. Copyright (c) 2007 Royal Meteorological Society.