Observations of Neutral Profiles of Wind Speed and Specific Humidity Above a Gently Rolling Landsurface

Abstract

Analyses were made of wind speed and specific humidity profiles under neutral conditions obtained by radiosoundings over the gently rolling terrain of the Little Washita Basin, Oklahoma. Inspection of the wind speed profiles showed that the regional (scale of 1 to 10km) roughness of this basin was z₀=0.45±0.21m, while the displacement height, d₀, was found to be 8.9m. The logarithmic layer of wind speed was observed to occupy the range, (38±43)z₀≤(z-d₀)≤(297±147)z₀ or (0.15±0.10)h_i where h_i is the height of the bottom of the capping inversion. This result is comparable with those of previous investigations for the lower limit of the range; however, this result also suggests that over this terrain h_i is the relevant length scale for the upper limit. Evaporation values at the regional scale were computed by combining the wind speed profiles with the specific humidity profiles. Comparison with surface flux measurements at Bowen ratio ground stations supports the idea that profiles in the neutral atmospheric surface layer aloft at around 100m above the ground are conditioned by upwind surface characteristics at the meso-γ scale.