Characteristics of the Cold Air Drainage on the Southeastern Slope of Mt. Shiouji in Dazaifu

Making local meteorological observations on the southeastern slope of Mt. Shiouji in Dazaifu on a calm clear night in April, 1993, we examined the actual conditions of cold air drainage and thermal belt on the hillside. After sunset, the cold air layer suddenly appeared and developed, and its thickness was kept being about 20 m through the night. The site where down-slope winds take off the surface was confirmed to be the central part of the thermal belt on the slope. The down-slope wind speed decreased gradually as the night progressed, which seems to be due to the ascent of the surface of the cold air lake that was developing above the foot of the mountain. The relation between the drainage wind speed and the potential temperature deficit in the cold-air-drainage layer can be explained by the equilibrium flow model by Mori et al. (1999).四王寺山南東斜面における冷気流の特徴として以下のような知見を得た. 1)日の入り後, 冷気層は急激に発達し, 夜間, その厚さは譯20mでほぼ一定であった. 2)冷気流が斜面を離れる場所は斜面温暖帯の中心部と一致した. 3)冷気流速は夜半から朝方にかけて漸減したが, 冷気湖面が次第に上昇し, その影響が現れた可能性が高い. 4)冷気流速と温位欠損の関係は平衡冷気流モデル(森ら, 1999)により説明できた