Abstract
Calculations of radiative transfer within a V-shaped valley show that the radiative cooling of the valley air is greater than the cooling over a flat surface. The measured cooling of a drainage flow in a deep, steep-walled valley is compared to calculations of radiative transfer within the same valley. It is found that cooling throughout the full watershed of the valley, instead of only within the steep walled part of the valley, must be considered to account for the energy loss of air passing through the valley. Some 10% to 20% of this energy loss occurs as a result of direct radiative cooling of the air.