抄録
In order to make clear the characteristics of cold air drainage, observations were carried out on the gentle slope of Mt. Neko in Nagano Prefecture, Japan. Period of the cold air drainage is defined as a period when the air temperature shows minus (plus) anomaly and the wind velocity plus (minus) anomaly from the moving mean of five terms. The results of the observations can be summarized as follows : (1) Three main maxima in the occurrence frequency (Fig. 5) of cold air drainage are generally seen in the night time in August. They are, (i) between 21h30m and 23h00m, (ii) 24h00m and 1 h30m, and (iii) 4h00m and 6h30m. However, four maxima are found for all observations including May and Decem-ber, and this additional peak is observed between 19h30m and 21 h00m. In all cases, the last maximum which occurs between 4h00m and 6h30m is the strongest and its occurrence in frequency is about 70%. (2) The directions of the cold air drainage converge within _??_45° of the mean direction, which coincides with the direction of maximum inclination of the slope. (3) During the cold air drainage, it is found, that the warm cores appear locally and they move from the lower part to the upper part of the slope with velocities of 0.3-0.8m/s. The occurrence of the warm core has not significant relation with the intensification of general wind of the upper layer. I t is thought, therefore, that the warm core is caused by sinking of warm air from the upper layer as the compensation flow of the cold air drainage
