HR: 0800h
AN: H31E-0693    [Abstracts]
TI: Large-Eddy Simulations of Forest Canopy Micro-Scale Structural Heterogeneity Effects on the Atmospheric Boundary Layer
AU: * Bohrer, G
EM: gb16@duke.edu
AF: Harvard University Center for the Environment, HUH, 22 Divinity Ave, Cambridge, MA 02138, United States
AU: Katul, g G
EM: gaby@duke.edu
AF: The Nicholas School for the Environment and Earth Science, Duke University, Box 90328, LSRC, Durham, NC 27708, United States
AU: Walko, R L
EM: robert.walko@duke.edu
AF: Department of Civil and Environmental Engineering, Duke University, Box 90287, Hudson 118, Durham, NC 27708, United States
AU: Avissar, R
EM: avissar@duke.edu
AF: Department of Civil and Environmental Engineering, Duke University, Box 90287, Hudson 118, Durham, NC 27708, United States
AB: The recently developed Regional Atmospheric Modeling System (RAMS)-based Forest Large-Eddy Simulation (RAFLES) is used to explore the effects of micro-scale structural heterogeneity of forest canopies on the Atmospheric Boundary Layer. This heterogeneity is represented by structural features such as differences between the heights and leaf densities of individual trees. The autocorrelation length scale of these features is smaller than the mean canopy height. The virtual canopy generator (V-CaGe) is used to generate a realistic canopy, based on observed canopy statistics from a hardwood stand in the Duke Forest, as a control case. Two different environments are considered: one is in the winter season characterized by moderate winds aloft, a sparse canopy and a slightly unstable boundary layer; the other is in the spring season with a dense canopy and a strongly convective boundary layer. The control case (under the two environments) is compared with two test cases simulating different levels of heterogeneity, with the same mean canopy properties and atmospheric forcing: (1) A horizontally homogeneous canopy; and (2) A heterogeneous canopy that also includes tree fall gaps. Micro-scale heterogeneity impacts the roughness properties, the effective drag coefficients, the displacement height, and the planar-averaged flow statistics. It also leads to higher-order effects pertaining to the spatial statistics of the ejection-sweep cycle generating correlations between micro-scale canopy features, flow statistics and fluxes, which persist up to five times the height of the canopy.
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 1632 Land cover change
DE: 1840 Hydrometeorology
DE: 3307 Boundary layer processes
DE: 3379 Turbulence (4490)
SC: Hydrology [H]
MN: 2007 Fall Meeting