Roughness length and drag coefficient at two MONTBLEX-90 tower stations |
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Authors: | Kusuma G. Rao |
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Affiliation: | (1) Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., 560 064 Bangalore, India |
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Abstract: | Using MONTBLEX-90 mean velocity data, roughness lengths and drag coefficients are estimated at Jodhpur and Kharagpur. At Jodhpur, since the surface is not uniform the roughness length is estimated separately in three different subsectors within the range of prevailing wind directions and averages to 1.23 cm in the sector between 200° and 230° which is relatively flat with no obstacles on the ground. At Kharagpur, where the terrain is more nearly homogeneous, the average value (for all prevailing wind directions) is 1.94 cm. The drag coefficient CD at Jodhpur shows variation both with the roughness subsector and with wind speed, the average over all directions increasing rapidly as themean wind speed Ū10 at 10m height drops according to the power lawC D = 0.05 Ū 10 t-1.09 in trie range 0.5 < Ū10 < 7 m s−1. At Kharagpur, the drag coefficient is smaller than at Jodhpur by nearly 50% for the same range of wind speeds (> 3 ms−1). |
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Keywords: | Monsoon trough boundary layer roughness length drag coefficient |
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