The Sensitivities of Nocturnal Cooling and Drainage Flow over an Inclined Topography to Meteorological, Ground Surface, and Topographic Conditions

Abstract

On the basis of results of slope and valley drainage flow models (Kondo and Sato, 1988; Sato and Kondo, 1988), a simple method is presented for the simultaneous evaluation of nocturnal cooling and drainage flow over slopes and in valleys under weak ambient wind conditions. Evaluations are made of the sensitivities of nocturnal cooling, drainage flow characteristics (velocity and thickness), and sensible heat transport by the drainage flow to the following conditions: meteorological conditions, thermal constant of the ground, surface aerodynamic properties and topographic features.
Due to the enhancement of sensible heat transport by the drainage flow, surface cooling of an inclined topography is smaller than that of a horizontal plain. The velocity of the drainage flow is sensitive to the conditions mentioned above, but its thickness is dependent only on the surface aerodynamic properties and the topographic features. The side-slope flow plays an essential role in the energy exchange between the atmosphere and a valley.
Available observations of nocturnal cooling and drainage flow support the present method.