Surface Water Vapor and Momentum Fluxes under Unstable Conditions from a Rugged-Complex Area

Abstract

Measurements were made of the profiles of mean wind velocity, of temperature, and of specific humidity in the unstable atmospheric boundary layer over macro-rough terrain; these data were obtained from radiosonde observations in a calibrated watershed of 3.2 km2 in the hilly Pre-Alps of Switzerland during the summer of 1982. The regional evaporation was reasonably well correlated (R = 0.7) with these profile measurements through a logarithmic height dependency between roughly 2h0 (where h0 ≈ 100 m is the mean height of the roughness obstacles) and 0.6h (where h is the height of the boundary layer above the mean valley level). The shapes of the profiles appear to be essentially independent of the Monin?Obukhov parameter (z? d0)/L, but they display a dependency on the wind shear aloft and on the value of (z0/h) (where z0 is the roughness height). Over this rugged surface the relative importance of mechanical turbulence, as compared to convective turbulence, is larger than over terrain with smaller (z0/h) for the same degree of instability of the atmosphere.