Terrain-induced effects on the ozone, temperature and water vapour daily variation in the upper part of the PBL over hilly terrain

Measurements of the daily variation of several meteorological and chemical parameters in the planetary boundary layer above the crest-height of a mountain-valley system of the Swiss Plateau are presented. On the basis of the observations, it is concluded that processes at the earth-atmosphere boundary are contributing strongly to the ozone losses, the increase inhumidity, and the cooling rates observed during night-time at these higher levels. Surface-layer effects are coupled to the upper part of the boundary layer by transport processes, which result from the orographic forcing of the mean wind field (i.e. occurrence of the phenomenon of blocking) and the interaction of mean flow with locally-induced wind systems. Thus the observations cannot be interpreted purely by local effects. In this part of the planetary boundary layer, the additional influence of processes due to the complex topography on a more regional scale is also felt. It is stressed that this coupling should be adequately represented in atmospheric pollution models of non-homogeneous terrain.