冬季における中国地方の天気界について

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タイトル別名
  • ON THE WINTER WEATHER DIVIDE IN THE CHÛGOKU REGION
  • トウキ ニ オケル チュウゴク チホウ ノ テンキカイ ニ ツイテ

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In Japan, characterized by the monsoons, a striking contrast can be found with respect to the climatic conditions especially in winter, between the regions along the Pacific and the Japan Sea coast.The winter monsoon brings forth much snowfall and cloudy weather in the latter region, while the fine weather prevails in the former.<br> The main purpose of this study is to find out where the winter weather divide most frequently appears in the Chûgoku Region, and to add some considerations to the obtained results. This survey was taken in the winter months from 1953 to 1955.<br> A weather divide can be distinguished by the fact that the weather is quite different from each other at the two adjacent points. Therefore, to draw a distribution map of the weather divide frequency, the following method was adopted: (1) Two points adjacent to each other are linked with a straight line on a map (Fig. 1) . (2) Frequencies of the divides during the period concerned are obtaind for every line. (3) The obtained values are reduced to an unit distance (12km), and those numerical figures are written at the middle point of each line. (4) In this way, two distribution maps showing the frequency of weather divide can be obtained. One is a map with respect to the divide between cloudy and snowy weather (Fig. 2), and the other, between fine and cloudy weather (Fig. 6).<br> I. On the divide as a southern limit of the precipitation area-Fig. 2-: (1) Two types of the precipitation area expansion can be classified in this region except its eastern district. One is commonly found in the northern half, with a tendency to expand southward from the Japan Sea coast-line, and the other is the mountain-area entirely separated from the coast. (2) When the former type predominates, the precipitation area invades into the Seto-uchi district, over the saddle of the mountain range (Fig. 3, h), and its southern limit coincides with (O-P). On the contrary, the latter type appears along the mountain range, having no relation with this saddle topography. (3) In both cases, the divide is apt to appear on (Q-R) and (M-N) in its eastern and western parts respectively. (4) Usually the precipitation area in the eastern district, limited by (Q-R), covers the whole Tottori Pref., extending from the Japan Sea coast-line to the Chfigoku mountain range (Fig. 4 shows the ferquency of precipitation when the divide appears on Q-R). (5) This precipitation area is often a part of that area covering the whole San-in district, or it is observed exclusively in Tottori Pref., and sometimes it comes out just at the same time as the appearance of precipitation area enclosed in the mountain-land of the western half of the Chiigoku Region. (Fig. 4). (6) With regard to the coastal districts along the Japan Sea, precipitation is more frequent in the eastern section than the middle and western parts, and marked difference in the frequency is found between Tottori and Shimane Prefectures.Thus a climatic sub-divide can be drawn along the border between these two prefectures.<br> II. On the divide as a southern limit of the cloudy weather-Fig. 6-:(1) The divide appearing on (E-D) is apt to expand to (B-A), with no divide occurring on (CE). (2) When it appears on (C-E), the NW monsoon prevails over the Chagoku Region, therefore the position of (C-E) is on the lee side of the mountain range (a-b). Fig. 7 shows the frequency of cloudy weather with the divide on (C-E). In this case, the W_??_NW wind has a tendency to bring forth a fine weather in Hiroshima (Fig. 8) (3) The cloudy weather area in the northern half of the region expands into the Seto-uchi district over the saddle of the mountain range (h), and its southern limit is often located on (E-H) (4) Its eastern limit varies with its position, while, the divide existing on (I-K) is commonly an eastern limit of the cloudy weather over the hilly area (f). Fig. 10 shows the frequency of cloudy weather when the divide exists on (I-K).

収録刊行物

  • 地理学評論

    地理学評論 31 (11), 655-665, 1958

    公益社団法人 日本地理学会

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