Mechanisms of up-valley winds

The basic physical mechanisms governing the daytime evolution of up-valley winds in mountain valleys are investigated using a series of numerical simulations of thermally driven flow over idealized three-dimensional topography. The three-dimensional topography used in this study is composed of two, two-dimensional topographies: one a slope connecting a plain with a plateau and the other a valley with a horizontal floor. The present two-dimensional simulations of the valley flow agree with results of previous investigations in that the heated sidewalls produce upslope flows that require a compensating subsidence in the valley core bringing down potentially warmer air from the stable free atmosphere. In the context of the three-dimensional valley-plain simulations, the authors find that this subsidence heating in the valley core is the main contributor to the valley plain temperature contrast, which, under the hydrostatic approximation, is the main contributor to the valley plain pressure difference that drives the up-valley wind.