HR: 0800h
AN: OS21C-1275    [Abstracts]
TI: Wind Stress Distributions on a Tree-Canopy Sheltered Lake
AU: * Thill, J
EM: thil0020@umn.edu
AF: Saint Anthony Falls Laboratory, University of Minnesota, 3rd Avenue Southeast at Mississippi River, Minneapolis, MN 55414 United States
AU: Porte-Agel, F
EM: fporte@umn.edu
AF: Saint Anthony Falls Laboratory, University of Minnesota, 3rd Avenue Southeast at Mississippi River, Minneapolis, MN 55414 United States
AU: Stefan, H
EM: stefa001@umn.edu
AF: Saint Anthony Falls Laboratory, University of Minnesota, 3rd Avenue Southeast at Mississippi River, Minneapolis, MN 55414 United States
AB: Wind stress over a lake is generally the most significant driver of whole-lake circulation and lake surface layer mixing. The spatial and temporal distribution of atmospheric flow velocity (and hence wind stress) over the lake is controlled by the roughness transition that the flow encounters as it crosses the shoreline onto the water surface. Well-established shear stress relationships for flat plates and open water surfaces indicate that experiments on flat plates may reasonably represent stress distributions over open water surfaces for wind speeds less than 10 m/s. Field measurements of wind speed profiles conducted on a frozen lake surface and at an agricultural transition of tall corn (1.7 m) to short rye stubble (less than 10 cm) suggest the presence of a blending layer that moderates the momentum flux that is transferred between the upper and lower internal boundary layers present immediately after a roughness transition. The data is compared to the blending layer models and the validity of various blending layer formulations is evaluated. The streamwise evolution of the surface internal boundary layer is quantified for the two cases at hand. This downwind evolution can be regarded as the result of interplay between a surface "equilibrium layer" and the growing "wedge" of the blending layer.
DE: 0399 General or miscellaneous
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting