TY - JOUR

T1 - Large eddy simulation of thermally induced oscillations in the convective boundary layer

AU - Letzel, Marcus Oliver

AU - Raasch, Siegfried

N1 - Funding Information: This research was supported by the German National Merit Foundation (Studienstiftung des deutschen Volkes) in Bonn, Germany, and German BMBF Grants 07ATF37-UH and 01LD0103. Calcula- tions were performed on the SGI/CRAY-T3Es of the Konrad–Zuse–Zentrum fu ̈r Informationstechnik (ZIB) in Berlin, Germany, and the Regionales Rechenzentrum fu ̈r Niedersachsen (RRZN) in Hannover, Germany. The authors wish to thank M. Kanda and R. Moriwaki (To- kyo Institute of Technology, Tokyo, Japan); Y. Noh (Yonsei University, Seoul, Korea); and D. Etling, T. Hauf, M. Herold, and J. Uhlenbrock (University of Han- nover, Hannover, Germany) for their valuable comments and suggestions. We are also grateful for the comments of Roni Avissar and two anonymous reviewers.

PY - 2003/9/15

Y1 - 2003/9/15

N2 - 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 ID 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 normalized with the boundary layer height, as well as power spectra and domain-averaged time series. The simulated mesoscale circulations were periodic. Vertical profiles and time series demonstrate that 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. Spectral analysis shows that the mesoscale circulations damp convection equally in all directions. A hypothesis of the oscillation mechanism is briefly discussed.

AB - 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 ID 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 normalized with the boundary layer height, as well as power spectra and domain-averaged time series. The simulated mesoscale circulations were periodic. Vertical profiles and time series demonstrate that 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. Spectral analysis shows that the mesoscale circulations damp convection equally in all directions. A hypothesis of the oscillation mechanism is briefly discussed.

UR - http://www.scopus.com/inward/record.url?scp=0142009662&partnerID=8YFLogxK

U2 - 10.1175/1520-0469(2003)060<2328:LESOTI>2.0.CO;2

DO - 10.1175/1520-0469(2003)060<2328:LESOTI>2.0.CO;2

M3 - Article

AN - SCOPUS:0142009662

VL - 60

SP - 2328

EP - 2341

JO - Journal of the Atmospheric Sciences

JF - Journal of the Atmospheric Sciences

SN - 0022-4928

IS - 18

ER -