Large-Eddy Simulation of a diurnal cycle in the turbulent Atmospheric Boundary Layer: Atmospheric stability and scaling issue

V. Kumar1,2, J, Kleissl1,2,4, M.B. Parlange1,2,5& C. Meneveau2,3, 1 Department of Geography and Environmental Engineering 2 Center for Environmental and Applied Fluid Mechanics, 3Department of Mechanical Engineering, The Johns Hopkins University, Baltimore MD 21218, 4 Now at New Mexico Tech University, Socorro, NM, USA, 5 EPFL, Lausanne, Switzerland

ABSTRACT: A simulation of a diurnal cycle of atmospheric boundary layer (ABL) flow over a homogeneous terrain is performed using Large Eddy Simulation (LES) with the Lagrangian scale-dependent dynamic subgrid-scale model. The surface boundary condition is derived from the field observations of surface heat flux from the HATS experiment (Horst et al 2004, Kleissl et al 2004). The simulation results display good general agreement with previous modelling and experimental studies with regard to characteristic features such as growth of the convective boundary layer by entrainment, nocturnal jet and multi-layered flow structure of the nocturnal regime. To gain a better understanding of the physical parameters affecting the statistics of the flow, we study the dependence of a subgrid parameter (Smagorinsky coefficient), resolved turbulent kinetic energy and resolved vertical velocity variance upon atmospheric stability. The profiles of these turbulent variables plotted as a function of Obukhov length show "hysteretic" behavior that implies non-unique dependence. The subsequent use of local Richardson number as the scaling parameter shows a decrease in this "hysteresis" but there is an increased scatter in the profiles with increasing height. Conversely, profiles plotted as a function of local Obukhov length (based on the fluxes at the local vertical level) show almost no "hysteresis" confirming the validity of Nieuwstadt's local scaling hypothesis. Although the local scaling hypothesis was formulated for the stable boundary layer, we find that it applies to the entire stability range of the diurnal cycle.

Water Res. Research 42, W06D09 (2006).

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Charles Meneveau, Department of Mechanical Engineering, Johns Hopkins University, 3400 N. Charles Street, Baltimore MD 21218, USA, Phone: 1-410-516-7802, Fax: 1-(410) 516-7254, email: meneveau@jhu.edu

 
Last update: 08/30/2008