Pressure drag and effective roughness length with neutral stratification |
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| Authors: | Stefan Emeis |
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| Institution: | (1) Institut für Meteorologie und Klimaforschung, Universität Karlsruhe/Kernforschungszentrum, Karlsruhe, F.R.G. |
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| Abstract: | A two-dimensional numerical mesoscale model is used to determine the pressure drag of sinoidal mountains and valleys in a neutral atmosphere. In the first part, pressure distributions and flow patterns for isolated obstacles are considered. For large aspect ratios, the pressure drag exerted by valleys becomes small compared to that of mountains. In the second part, interactions between several obstacles are investigated. For mountains, the drag on downstream obstacles is reduced considerably by the first obstacle when the obstacles are close together. For valleys there is a slight increase of the average drag exerted by each obstacle. In the limit for a large number of obstacles, average drag exerted by one mountain is equal to average drag for one valley. For smaller aspect ratios, this average drag can be entered into the resistence law from the Rossby number similarity theory to yield an  effective roughness length . |
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