Thermals in the Numerical Laboratory

Abstract

The atmospheric boundary layer in blue thermal conditions is investigated by means of Large Eddy Simulation (LES) on a personal computer, in model cases of increasing (but limited by computing capacity) complexity. Despite the high idealization, and without large-scale forcing other than geostrophic wind in the free atmosphere, the resulting flow patterns match with aeronautical practice and literature. Strong thermals are joined by small thermals, originating from illuminated slopes and asphalt surfaces on the ground. Weaker thermals emanate from vegetation areas at a sufficient distance from asphalt. The drier the ground and the lower the transpiration of the vegetation, the stronger the thermals. Above forests, thermals are stronger than above grass surfaces. In the absence of wind, air sinks over water bodies.