Abstract
Surface roughness parameters were determined for harvested wheat fields over level terrain at the US Department of Energy's Cloud and Radiation Testbed (CART) site in north-central Oklahoma. Measurements of wind speed and temperature were made by radiosondes and instruments mounted on 2 and 10m towers during neutral and unstable atmospheric conditions in the atmospheric surface layer. Surface temperatures were measured radiatively over 750m trajectories. Roughness heights were calculated for the region using the Monin–Obukhov similarity theory. The scalar roughness and the local momentum roughness were determined using wind speed measurements at 10m and temperature measurements at 2m combined with eddy correlation measurements for u∗. The scalar roughness zoh was determined to be 0.0021 and 0.0038m for the nadir and the off-nadir viewing angle, respectively. It was estimated that the displacement height d is negligible. A regional momentum surface roughness of zo=0.15m was determined by means of the radiosonde profiles. Good agreement (r=0.92) between measured and calculated sensible heat flux values was found using an independent data set of radiosonde profiles.
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