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.