The formation and destruction of inversion layers within a deep valley

The technique of large-eddy simulations has been used to investigate therma lly driven local circulations in deep valleys for a complete diurnal cycle. A soil model simulates the thermal forcing at the ground, which depends on the season, the soil characteristics, the valley orientation, and the atmo spheric variables. The scales of interest are characteristic of an urban site located in a mou ntainous area, and the research focuses on low wind conditions without the influence of large-scale pressure gradients. This study highlights the infl uence of the season on the mechanisms responsible for the formation and the destruction of the thermal inversion layer. The spatial distribution of th e convective boundary layer (CBL) within the valley is directly influenced by the season because of the variation of the solar warming. In summer, the altitude of the top of the CBL remains approximately constant across the v alley, whereas in winter,this altitude varies with its location within the valley.