Sensitivity Tests of a Surface-Layer Windflow Model to Effects of Stability and Vegetation.
Environmental research papers,
AIR FORCE GEOPHYSICS LAB HANSCOM AFB MA
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This study examines the sensitivity of surface-layer windflow over gently rolling terrain to different stability conditions, both with and without the effects of vegetation used to modify terrain heights and determine surface roughness. The numerical model used produces simulations of surface-layer windflow by using Gausss Principle of Least Constraints to allow an initially uniform windfield to adjust to topography and buoyancy forces while conserving mass. The model experiments used simulated meteorological data at only one observation point and detailed terrain and vagetation data on a 51-by-51 grid with 100 m spacing for an area covering 5 by 5 km over the Fort Polk Military Reservation in Louisiana. Results show that the model simulates topographically induced flows such as cold air drainage and upslope flow, despite the simple physics employed. We also show that the presence to tall vegetation over the area mainly coniferous and deciduous trees alters the flow patterns under various stability conditions. These effects are shown to be caused primarily by changes in the area of chemical transport and diffusion, because they mean that even gently rolling terrain influences the surface windflow, and that tall vegetation has a considerable influence as well.