月山の強風砂礫 斜面における通年気象観測と地形形成環境 Year-Round Meteorological Observations and Geomorphic Processes on a Wind-Swept Alpine Slope on Mount Gassan, Northern Japan
Microclimates and geomorphic processes on a wind-swept alpine slope (1, 805m asl) were evaluated on the basis of year-round observations of air temperature (1995 to 1996), ground temperatures (1995 to 1996), precipitation (1995 and 1996 summer), and wind velocity (1995 summer). Although the data were incomplete owing to mechanical problems with instruments, they are worth reporting. This is because few meteorological observatories are established in alpine areas in Japan. The followings are the main results of this study.<br> Air temperature: The maximum monthly mean air temperature of 13.9°C was recorded in August. The first freeze-thaw day of autumn 1995 occurred in early October. Air temperature remained steadily subzero from mid-November to late April 1996, and the minimum monthly mean of 8.8°C occurred in February. The data during the winter, however, should be treated as reference values because of the possible effect of snow and the rime ice coat on the insolation shelter. In comparison with the free-air data over Akita, 135km north of Gassan, the records from the observation site are estimated to be about several degrees centigrade higher than the true values. The mean annual air temperature at the site is thus considered to be lower than 0.9°C.<br> Ground temperatures: The maxima of the monthly mean ground temperature of 14.0°C and 13.9°C were recorded in August at depths of 2 and 20cm, respectively. A total of 15 freeze-thaw cycles took place at a depth of 2 cm from mid-October to mid-November. In contrast, no freeze-thaw cycle was recorded at a depth of 20cm in the autumn. Seasonal frost formed on the ground from mid-November to late April, and a total of 15 freeze-thaw cycles again occurred at a depth of 2cm from late April to mid-May.<br> Wind velocity: The maximum monthly mean wind velocity of 13.3m s<sup>-1</sup> was recorded in August. The appearance ratio of wind velocity over 5.0m s<sup>-1</sup>, attained 98%. The maximum hourly velocity was about 31m s<sup>-1</sup>, and strong winds were usually associated with the passing of cold/warm fronts and typhoons.<br> <i>Precipitation</i>: The observed meteorological precipitation was converted into hydrological values. Total amounts from July to September 1995 and 1996 were 779.5mm and 620.9mm, respectively. The daily and hourly maxima during the two observation periods were 73.1mm and 23.2mm, respectively. Similar to strong winds, most strong rainfalls were related to the passing of cold/warm fronts and typhoons.<br> Deflation scars several decimeters high well developed around the observation site. The meteorological records and our visual observations focusing on geomorphic processes imply that the retreat of such scars occurs intermittently from spring to autumn, although the contribution of deflation must also be evaluated.
- 地理学評論. Ser. A
地理学評論. Ser. A 70(10), 676-692, 1997-10
The Association of Japanese Geographers