Gravity Wind on a Snow Patch

[摘要] An occurrence of a gravity wind was found on a snow patch of smaller than 1.2km in length, on a warm summer day. The fundamental properties of this wind obtained from the observation are as follows. The maximum wind speed (Umax) was 1.5 to 4.0m/sec., and the height of the maximum wind speed (Zmax) was between 0.7 to 1.2m above snow surface. The Zmax and Umax had a linear relation. The wind speed of the gravity wind at a certain height, which can be considered to be proportionate to Umax was stronger when the difference of the air temperature between the free air and the cooled air layer above the snow surface was larger. The wind speed of the gravity wind was stronger at lower parts of the snow patch, having a relation of U∞√l where U is the wind speed and l is the distance from the upper end of the snow patch. The occurrence of the gravity wind was controlled by the strength of the general wind in the valley. It occurred only when the general wind was weak.The vertical profile of the observed wind speed can not be explained by the classical theoretical profile obtained by Prandtl (1952), but can be explained by the empirical profile obtained by Martin (1975).

[学科分类] 大气科学