Surface Energy Balance of Bare Soil as Influenced by Wetting and Drying

摘要

A bare soil surface of Adelanto clay loam was allowed to dry superficially and then flooded with 11 cm of water. Physical events over, at and below the surface were recorded continuously throughout eight days, beginning with the day before flooding. The terminal condition was close to the original one. The experiment took place in April-May 1966 in Phoenix, Arizona during a period of stable, clear and dry weather. When the surface was dry, net radiation and soil heat flow were the principal energy transfer processes. When the soil surface was wet, net radiation and latent heat transfer predominated, but soil heat flow was still more important than sensible heat transfer in the air. The last quantity did not change much in size or magnitude as result of flooding and remained negative during the daylight period. A surprising result was obtained for the period during which the surface first became dry, firm and lighter in color. Though net radiation was decreased, evaporation continued at the potential rate and large, positive values of sensible heat flux in the air were measured. These values did not agree with the measured differences between surface and air temperature, but it was also noted that any aerodynamic method, used to calculate the sensible heat flow in the air from surface temperatures, failed utterly. Excellent predictions of the latent heat flux during wet surface conditions were obtained with the Dalton-log law model and also with the combination model. Less accurate, but still acceptable prediction followed from the Bowen ratio method. (Author)