日本における秋雨期の季節推移の特徴と年々変動

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書誌事項

タイトル別名
  • Seasonal Transition and Year-to-Year Variations of the Autumn Rainy Season in Japan
  • ニホン ニ オケル アキサメキ ノ キセツ スイイ ノ トクチョウ ト ネンネン ヘンドウ

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抄録

The autumn rainy season called akisame is one of the two major rainy seasons in Japan. The aim of this study is to clarify the characteristics and causes of the akisame, paying attention to the seasonal transition and the year-to-year variations of the frontal frequency over East Asia during August to November. This study was carried out using the National Center for Environmental Prediction reanalyses data. The frontal frequency is defined as the percentage of the occurence in the surface weather map published by the Japan Meteorological Agency from 1979 to 2000.<br> In the seasonal march of the frontal frequency distribution, some abrupt changes are recognized. Concerning these changes, the akisame is divided into three periods: the early (Sept. 3-Sept. 12), the mid (Sept. 13-Oct. 7), and the late autumn rainy seasons (Oct. 8-Oct. 22). In each period of the rainy season, the areas with the largest amount of precipitation closely correspond to the high-frequency zones of fronts.<br> In the akisame, the seasonal marches of the circulation patterns at 850 hPa are characterized by the four pressure systems: the Pacific high, the Indian monsoon low, the high over China, and the low-latitude trough from the South China Sea to the Philippine Sea. Two mid-latitude troughs which exist near Japan (100-150°E) and near the mid-Pacific Ocean from the Bering Sea (160°E-160°W) are also important. The development of these pressure systems and mid-latitude troughs cause the differences in the frontal frequency distribution in the three periods of the akisame. These seasonal marches are also accompanied by seasonal changes in the mid-latitude westerly and the subtropical jet near the Tibetan Plateau at 500 hPa.<br> The year-to-year variations in the frontal frequency are closely connected with the development of the Pacific high and the low-latitude trough from the South China Sea to the Philippine Sea. These pressure systems seem to be related to typhoon activities. The place and time that the Pacific high, the low-latitude trough from the South China Sea to the Philippine Sea, and the mid-latitude trough expanded from the Bering Sea have a strong influence on the timing of the akisame. The subtropical jet near the Tibetan Plateau does not contribute so directly to the year-to-year variations in the frontal frequency.

収録刊行物

  • 地理学評論

    地理学評論 76 (13), 935-956, 2003

    公益社団法人 日本地理学会

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