Abstract
Three-dimensional distributions of wind speed and temperature in a V-shaped valley covered with a pasture and scattered shrubs were continuously observed. The typical drainage flows were observed in the cold layer when the wind speed at a ridge is less than 2.6m/s and mainly 79 cases of such a drainage flow were analyzed. The cold layer in the valley is divided into two parts. The upper part is a drifted cold layer and a lower one is a primary cold layer. The vertical profile of potential temperature in the drifted cold layer is represented by a linear function of height. The wind profile of a typical drainage flow is parabolic rather than Prandtl-like. The wind speed below the level of maximum wind does not seriously change with a fetch, but the wind speed in the upper part of the cold layer outstandingly increases with a fetch. The maximum wind speed of drainage flow increases in proportion to a square root of cooling strength. Also, the height of cold layer at the fetch of 800m slightly increases with a cooling strength. The horizontal heat flux toward the downstream along the valley axis changes with a fetch and took the values of -1.01MW and -1.77MW at the fetches of 400m and 800m, respectively. From the difference of horizontal heat flux between two cross sections of valley, the bulk coefficient of heat transfer, CH, and the reciprocal of the interfacial Stanton number, BH-1, were estimated at 0.01 and 20, respectively.
