Evaporation at night.

Abstract

Direct measurements with a dew balance of evaporation from a short-grass surface were compared with humidity gradients in the grass over about 5 weeks in autumn, 1953. At night, when the air in the cover was unsaturated, evaporation occurred by the diffusion of water vapour from the soil surface through a thin layer of air in which the transfer coefficient was seldom greater than twice the molecular value. The rate of evaporation was about 0.04 mm/hr. Evaporation of this order will occur whenever cold radiating leaf surfaces are found within a few cm of a warmer soil surface. Even with taller crops, where temperature and humidity gradients are smaller, greater mixing of the air within the crop may produce fluxes of the same order. (Abstract retrieved from CAB Abstracts by CABI’s permission)