著者

黒坂 裕之

出版者

公益社団法人 日本地理学会

雑誌

地理学評論 (ISSN:00167444)

巻号頁・発行日

vol.55, no.11, pp.779-788, 1982

被引用文献数

1

---

Meteorological satellite pictures show the cloud lines which appear around the Japan Islands under a winter monsoon situation. The cloud lines can be classified into four types. The first type is the cloud lines from the open sea surrounded by cold land or sea ice areas. The second type is the cloud lines over the Pacific Ocean, starting from the cloud area over the Japan Sea, and going through the lowlands between the mountain ranges of the Japan Islands. The third type is the cloud lines which start i n the Japan Sea and continue to the western coast of the Japan Islands. From there no cloud lines are seen until reaching the eastern coast to the lee of the gaps in the mountain ranges of the Japan Islands, and continue out over the Pacific Ocean. The fourth type is the cloud lines to the lee of the mountains.<br> The purposes of the present study are to describe the forms of the cloud lines and also to compare the atmospheric condition in relation to the appearance of the cloud lines. The satellite data used in this study are visible photographs taken from the polar-orbit satellite, NOAA-5. The visible information was used to determine the existence and location of cloud lines. The periods of this study are December, 1976 to March, 1977 and December, 1977 to March, 1978.<br> From the visible information, we can determine eight major areas of cloud line appearance. Most of the cloud lines appear under the winter monsoon situation. A circle with its center at a point on the cloud line and with radius of 400 km can be drawn. If a center of low pressure or a center of high pressure appears within the circle, a cloud line does not appear.<br> The cloud lines to the east of Sendai, in northern part of Japan for example, are described by the relationship between the directions of the lower wind and the cloud line direction. The cloud line to the east of Sendai belongs to the third type of cloud line. The reason why these cloud lines were selected is that the aerological station is located at Sendai, upward of the cloud lines. It is easy to compare the cloud line direction with the wind direction at a lower level. The mean value and standard deviation of cloud line direction is 295&deg; and 15&deg;, ranging from 280&deg; to 320&deg;. On the other hand, the mean values and standard deviations of wind direction at the 900, 850 and 800 mb levels are 295&deg;, 295&deg; and 290&deg;, and 10&deg;, 10&deg; and 10&deg;, respectively. The mean values of the cloud line direction are equal to those of the wind direction, but the coefficients of correlation for each case are very low. However, the scatter diagrams showing the relationship between the cloud line direction and the wind directions show close correlations, except for the cases having 280&deg; of cloud line direction. The regression equations are shown as follows:<br> D₉₀-290=1.2 (Dir-290)-10.0 (r=0.73)<br> D₈₅-290=1.0 (Dir-290)-5.0 (r=0.69)<br> D₈₀-290=0.8 (Dir-290)-5.0 (r=0.59) where D₉₀, D₈₅ and D₈₀ represent the wind directions at the 900, 850 and 800mb levels, respectively. &ldquo;Dir&rdquo; represents the cloud line direction. The coefficient of correlation is shown by the &ldquo;r&rdquo; in parenthesis.<br> The cloud free distance means the distance from the coastal line to the upward appearance point of the cloud line along the cloud line direction. It is considered that the longer the cloud free distance is, the stabler the atmosphere around the cloud line is. The mean value of the cloud free distance to the east of Sendai and its standard deviation are 75km and 50km, ranging mainly from 50km to 100km. As an index of atmospheric stability, the temperature difference between the 850mb level and the mean sea surface temperature is used. Cloud lines do not appear under conditions when the temperature difference is lower than 21&deg;C.