EARTHSC 2C03 Lecture Notes - Lecture 9: Negative Number, Richardson Number, Rhode Island Route 2
15 Feb 2017
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Document Summary
Rough surfaces such as trees and buildings exert frictional drag on horizontal wind speed. Wind speed near the ground surface is reduced because of surface roughness effects (see figure 2. 10a, oke, 1987). Frictional influence on wind speed depends on the roughness of the surface. Rougher surfaces such as forests and cities influence a deeper layer of air above them. The force exerted on the surface by air being dragged over it is called surface shearing stress ( ). It has units of force per unit area i. e. pressure (pa). Because of this frictional influence the wind speed decreases as we approach the surface. The shearing force exerted by moving air is transmitted downwards. Momentum mean horizontal wind sped u where is air density and u is mean horizontal wind speed. Since density is relatively constant, momentum is proportional to the wind profile. In the turbulent surface layer, the momentum flux is expressed by ficks.
