HR: 1330h
AN: H42A-1064    [PDF]
TI: A-priori Laboratory Studies to Improve Modeling of Land-Atmosphere Interactions Over Heterogeneous Surface Conditions
AU: * Carper, M A
EM: carper@msi.umn.edu
AF: Saint Anthony Falls Laboratory, University of Minnesota, 3rd Avenue at the Mississippi River, Minneapolis, MN 55414 United States
AU: Port‚-Agel, F
EM: fporte@umn.edu
AF: Saint Anthony Falls Laboratory, University of Minnesota, 3rd Avenue at the Mississippi River, Minneapolis, MN 55414 United States
AU: Stoll, R
EM: stolli@msi.umn.edu
AF: Saint Anthony Falls Laboratory, University of Minnesota, 3rd Avenue at the Mississippi River, Minneapolis, MN 55414 United States
AB: A more accurate understanding of the subgrid-scale physics is essential to improve large-eddy simulation (LES) and its ability to capture the effect of heterogeneous surface conditions on fluxes of momentum, heat, and moisture in the atmospheric boundary layer (ABL). The main limitation of LES to produce the correct ABL physics over varying land surface conditions is due to errors in the parameterization of the subgrid-scale (SGS) stresses representing the effect of the unresolved (subgrid) scales on the resolved scales. In particular, SGS stresses need to be specified within the boundary layer (using a SGS model) and at the surface (through a boundary condition). Direct studies of SGS stresses have been performed by means of {\it a priori} wind tunnel experiments with prescribed flow properties over heterogeneous surface conditions of known roughness and length scales. Specifically, high-resolution, two-dimensional velocity fields were obtained in the turbulent boundary layer over a heterogeneous surface using particle image velocimetry. The velocity fields were spatially filtered (in 2-D) and used to calculate filtered (resolvable) velocities and SGS stresses. These filtered velocities were used to compute the local strain rate tensor and to estimate the SGS energy dissipation rate. To study the surface boundary condition, the velocity fields were synchronized with surface-shear (filtered) stress events as determined from an array of nine hot-film sensors mounted flush to the surface. Results, based on the SGS energy dissipation rates, indicate the importance of coherent structures in the transfer of energy between the unresolved and resolved scales of motion relevant to SGS modeling. These results are used to evaluate existing SGS models in simulations over heterogeneous surfaces.
DE: 3210 Modeling
DE: 3307 Boundary layer processes
DE: 3322 Land/atmosphere interactions
DE: 3337 Numerical modeling and data assimilation
DE: 3379 Turbulence
SC: Hydrology [H]
MN: 2003 Fall Meeting