SURFACE-LAYER FLUXES, PROFILES, AND TURBULENCE MEASUREMENTS OVER UNIFORM TERRAIN UNDER NEAR-NEUTRAL CONDITIONS

An atmospheric surface-layer experiment over a nearly uniform plowed h eld was performed to determine the constants in the flux-profile simil arity formulas, particularly the von Kaman constant. New instruments w ere constructed to minimize flow distortion effects on the turbulence measurements and to provide high-resolution gradient measurements. In addition, a hot-wire anemometer directly measured the turbulent kineti c energy dissipation rate. An average value of the von Karman constant of 0.365 +/- 0.015 was obtained from 91 runs (31 h) in near-neutral s tability conditions. However, four near-neutral runs when snow covered the ground gave an average value of 0.42. This result suggests that t he von Karman constant depends on the roughness Reynolds number, which may resolve some of the differences in previous determinations over d ifferent surfaces. The one-dimensional Kolmogorov inertial subrange co nstant was found to have a value of 0.54 +/- 0.03, slightly larger tha n previous results. The flux-profile relations for momentum and temper ature variance were evaluated, and humidity variance data behaved simi larly to temperature. Dissipation of turbulent kinetic energy was foun d to be less than production under near-neutral conditions, which sugg ests that turbulent or pressure transport may be significant.