EVALUATION OF EVAPORATION FLUX UNDER QUASI-UNSTEADY WIND VELOCITY

Abstract

The present paper describes a new method to precisely calculate hourly evaporation flux under quasi-unsteady wind velocity using the wind tunnel that can supply a set of high/low speed winds by turns for every set-up period. Soil columns was used for the evaporation experiment and Chao soil and Toyoura standard sand were used for the experiment. The difference in the hourly evaporation flux, E_vh, became no less than 12-18% by changing the combination of the high/low speed winds, regardless of the kind of soil, although the average wind velocity, V_wm, was the same for all the wind-velocity combinations. This fact is attributed to the nonlinearity of the relation between the evaporation coefficient, α_v, and wind velocity. It is found that E_vh calculated using α_v for the high and low wind velocities is more accurate than that calculated using α_v for V_wm.