2002 Volume 46 Pages 67-72
Mesoscale circulations induced by differential boundary layer heating due to surface inhomogeneities on scales of 5km and more can significantly change the average properties and the structure of the convective boundary layer (CBL) as well as trigger off temporal oscillations. The results of one of the first numerical case studies using Large-Eddy Simulation (LES) on the mesoscale suggest that mesoscale circulations exhibit a considerably larger average kinetic energy than convection under homogeneous conditions.
This case study uses the Hannover LES model PALM with prescribed 1D sinusoidal surface heat flux variations on wavelengths from 2.5 to 40km. The resulting mesoscale circulations are analyzed by means of domain-averaged cross-sections, time averaged and normalized with the boundary layer height, as well as domain-averaged time series.
The simulated mesoscale circulations were periodic. Vertical profiles and time series demonstrate mat the onset of the mesoscale circulation triggers off a temporal boundary layer oscillation, whose period and amplitude depend on the surface heat flux perturbation wavelength and amplitude and on the background wind component perpendicular to the surface inhomogeneity orientation. A hypothesis of the oscillation mechanism is briefly discussed.
