Diurnal Mountain Wind Systems

Diurnal mountain wind systems are local thermally driven wind systems that form over mountainous terrain and are produced by the buoyancy effects associated with the diurnal cycle of heating and cooling of the lower atmospheric layers. This chapter reviews the present scientific understanding of diurnal mountain wind systems, focusing on research findings published since 1988. Slope flows are examined first, as they provide a good introduction to the many factors affecting diurnal mountain wind systems. The energy budgets governing slope flows; the effects of turbulence, slope angle, ambient stability, background flows and slope inhomogeneities on slope flows; and the methods used to simulate slope flows are examined. Then, valley winds are reviewed in a similar manner and the diurnal phases of valley and slope winds and their interactions are summarized. Recent research on large-scale mountain-plain wind systems is reviewed, with an emphasis on the Rocky Mountains and the Alps. Winds occurring in closed basins and over plateaus are then discussed, and analogies between the two wind systems are outlined. This is followed by a discussion of forecasting considerations for diurnal mountain wind systems. Finally, the chapter concludes with a summary of open questions and productive areas for further research.