Thermal asymmetry and cross-valley circulation in a small Alpine valley

Wind observations from a small Alpine valley are used to investigate the problem of cross-valley winds. The observed daytime windfield is a superposition of dynamically and thermally forced cross winds. Prevailing cross winds above the valley result in a recirculation cell above the lee slope. The return flow is strengthened or weakened by thermal effects that induce a wind that blows from the shaded to the sunny side of the valley. The reaction time of the thermally induced cross winds is only 4 min. The horizontal and vertical motions of the cross-valley circulation transport heat in such a way that the insolation differences between the two sides of the valley are nearly equalized.