Large Eddy Simulation of Thermally Induced Oscillations in the Convective Boundary Layer

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Abstract
Mesoscale circulations induced by differential boundary layer heating due to surface inhomogeneities on scales of 5 km 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 affects turbulent transport processes and should be accounted for in larger-scale models even if their turbulence parameterizations rely on homogeneous control runs of high-resolution models. This case study uses the Hannover parallelized large eddy simulation model (PALM) with prescribed 1D sinusoidal surface heat flux variations on wavelengths from 2.5 to 40 km. The resulting mesoscale circulations are analyzed by means of domain-averaged cross sections, time averaged and normali... Abstract Mesoscale circulations induced by differential boundary layer heating due to surface inhomogeneities on scales of 5 km 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 affects turbulent transport processes and should be accounted for in larger-scale models even if their turbulence parameterizations rely on homogeneous control runs of high-resolution models. This case study uses the Hannover parallelized large eddy simulation model (PALM) with prescribed 1D sinusoidal surface heat flux variations on wavelengths from 2.5 to 40 km. The resulting mesoscale circulations are analyzed by means of domain-averaged cross sections, time averaged and normali...