干旱区生态环境知识资源中心

Using observational data acquired during the Monsoon Trough Boundary Layer Experiment (MONTBLEX-90), the drag coefficient C-D is estimated over two land stations, Jodhpur (arid region) and Kharagpur (moist region), by eddy correlation of velocity data from sonic anemometers. At low winds C-D varies with wind speed according to a power law, which at Jodhpur takes the form C-D=0.04 (U) over bar(10)(-1.06) ((U) over bar(10) being the mean wind speed at 10 m). The large values of the drag coefficient at low winds are associated with both near-neutral and strongly unstable situations. On the other hand, the C-D values at Kharagpur are less than at Jodhpur by nearly 50% for wind speeds > 3ms(-1), and cannot be explained by the different roughness lengths at the two sites.