An Observational Study of the Effects of Ambient Stratification and Wind on the Cold-Air-Drainage (CAD) Wind Speed on a Grass-Covered Slope of Mt. Kuju

Abstract

Observations of cold-air-drainage (CAD) winds were made on a geometrically simple grass-covered slope of Mt. Kuju (Oita, 1,787 m ASL), with the average inclination of 7°. Observations were made on 12 nights, with the results summarized as follows: (a) The direction of CAD winds at an observation station differed from that at another station on the slope, and the change in the angle of direction between the two stations had a bimodal frequency distribution. (b) When a mixed layer is capped by a strong inversion, CAD winds accelerated on the leeward slope and decelerated on the windward slope. (c) When ambient potential temperature increased linearly with altitude, CAD winds decelerated on the leeward slope and accelerated on the windward slope. The mechanisms responsible for these phenomena are shown, based on a few hypotheses.