Heterogeneous Nocturnal Cooling in a Large Basin Under Very Stable Conditions

Abstract

Large basins with relatively wide floors experience heterogeneous nocturnal cooling due to the diversity of the topography and the land use within the basin. Near moun- tain ranges the drainage flows prevail, but in low areas, river valleys or embedded plateaux, the actual rates of cooling differ as does the behaviour of the local flows in the first few metres above the surface. In this study, the temporal and spatial heterogeneity of the surface cooling is inspected through the analysis of satellite radiative surface temperature, data from a meteorological network and a tall tower. The organisation of the flow within the basin is also studied by means of a high-resolution numerical mesoscale simulation. Although the basin cools almost as a unit, there exists a large diversity of local regimes. Vertical profiles from the mesoscale simulation are analysed and grouped according to their wind structure and stratification.