Influence of a Distantly Located Typhoon, a Weak Westerly Trough and Orography on the Intense Rainfall on 14-15 September 1965 over Gifu and Fukui Prefectures of Japan

摘要

Influence of a distantly located typhoon (TY), a weak westerly trough, and orography on the intense rainfall on September 14-15, 1965 over Gifu and Fukui Prefectures (~36°N, 137°E) in central Japan is studied by using European Center for Medium-Range Weather Forecasts 40-year reanalysis data and upper, surface, and local rain-gauge observation data. Prior to the intense rainfall, a long arc-shaped moisture front was intensified on September 13 along the northern periphery of the outer circulation of TY Tix (6524), which was distantly located from Japan. A rainfall of 50?100 mm d~(-1) occurred in a long rainbelt along the Pacific coast of Japan, associated with the low-level convergence in the moisture front. A small depression formed over the Japan Sea on September 14 under the influence of a weak westerly shortwave trough in the middle troposphere. In the lower troposphere, a Λ-shaped trough extended from the outer circulation of the TY toward the depression and the moisture front protruded locally northward to the depression. Concurrently, with the protrusion of the moisture front, ameso- α-scale (~500 km) intense rainfall area protruded northward. In the meso- α-scale intense rain area, a south?north oriented narrow rainband formed along the east side of Suzuka-Ibuki Mountains on September 14. A maximum precipitation of ~800 mm d~(-1) occurred in the rainband. This case may fall under "intense rainfall remotely affected by TY." However, the present case is different from other cases studied in previous articles in that very intense precipitation occurred in a narrow south?north oriented rainband formed along mountains under the influence of the weak westerly shortwave trough.