THE EFFECT OF SLOPE-ASPECT ON TURBULENT TRANSFER IN AN ALPINE FELLFIELD: NIWOT RIDGE,FRONT RANGE,COLORADO

This study investigates the impact of local convergence and divergence of air on turbulent transfer at a mid-latitude alpine fellfield site. Pairs of simultaneous wind and temperature profile measurements on a knoll crest and primary slope (aspect =0, 90, 180, and 270°) are analyzed assuming the logarithmic law. Friction velocity (u*) and roughness length (z₀) vary systematically from windward to leeward slopes. General relationships of the form u* = f(u) are derived for conditions of westerly flow with wind speed (u) ranging between 2 and 24 m s^-1. Coefficients in the empirical equations for estimating u* at sites on the knoll from wind speed measurements on the crest vary in a consistent manner with respect to local convergence and divergence. Large differences in z₀ values between windward and leeward sites correspond with contrasts in surface temperature.