Wind velocity measurements in the neutral boundary layer above hilly prairie

Abstract

The Flint Hills region in eastern Kansas is characterized by strongly dissected rolling to hilly terrain with on average about 25 m of relief between steep ridges and valleys, and with ridges typically separated by distances of the order of 600 m. Intensive radiosonde observations during summer and fall of 1987 allowed the determination of some aspects of the wind regime in the region. For an assumed ground‐surface reference of 330 m above sea level (asl), analysis of neutral profiles yielded a value z0 = 1.05(±0.51) m, approximately; this value was obtained with an assumed displacement height d0 = 25.7z0, as suggested by the density of the terrain roughness. The corresponding logarithmic law was found to hold over the height range 50(±19) m < z − d0 < 202(±101) m (where z is above the same ground surface level). Good agreement (r = 0.92) was obtained between the u* values derived from these wind profiles and values determined independently from the corresponding humidity profiles. Some large wind speeds were observed; for instance, the resulting mean surface shear stress was u* = 0.82(±0.24) m/s.