HR: 1330h
AN: H42A-1063    [PDF]
TI: Scale-Dependent Dynamic Models for LES of the Atmospheric Boundary Layer Over Heterogeneous Surfaces: Sensitivity to Averaging Schemes
AU: * Stoll, R
EM: stolli@msi.umn.edu
AF: St. Anthony Falls Lab, Department of Civil Engineering University of Minnesota, 2 3rd Ave SE, MInneapolis, MN 55414 United States
AU: Port‚-Agel, F
AF: St. Anthony Falls Lab, Department of Civil Engineering University of Minnesota, 2 3rd Ave SE, MInneapolis, MN 55414 United States
AU: Bjelogrlic, N
AF: St. Anthony Falls Lab, Department of Civil Engineering University of Minnesota, 2 3rd Ave SE, MInneapolis, MN 55414 United States
AB: Large eddy simulation (LES) has become an increasingly popular tool to study the effect of surface heterogeneity on regional fluxes, which need to be parameterized in weather and climate models. Accurate estimation of these fluxes is limited by the ability of the LES subgrid scale (SGS) model to properly represent the turbulent subgrid scale fluxes of momentum and scalars (e.g. heat and water vapor). A common approach used in LES of the atmospheric boundary layer (ABL) is to parameterize the SGS stresses with an eddy-viscosity model and the SGS scalar fluxes with an eddy-diffusion model. Each of these models requires the specification of one parameter: the Smagorinsky coefficient and the SGS Schmidt number in the eddy viscosity and eddy-diffusion models, respectively. These parameters can be computed dynamically at every time step and position in the flow based on the resolved LES fields with a procedure developed by Germano (1991) and recently generalized by Port‚-Agel et al (2000, 2003) to account for scale dependence of the coefficients. In order to guarantee numerical stability, these dynamic models require some degree of spatial averaging of the variables involved. For the case of boundary layers over homogeneous surfaces the averaging is performed over horizontal planes. In this study we use the scale-dependent dynamic model with different local averaging schemes (more suitable than plane averaging for non-homogeneous boundary layers) in simulations of the ABL over heterogeneous surface conditions. Sensitivity of our results to the averaging scheme is explored for different surface patterns of aerodynamic roughness and scalar fluxes. Emphasis is placed on the spatial distribution of the dynamic model coefficients, scale-dependence parameters and resolved turbulent fluxes.
DE: 3307 Boundary layer processes
DE: 3322 Land/atmosphere interactions
DE: 3379 Turbulence
SC: Hydrology [H]
MN: 2003 Fall Meeting