大雪山雪壁雪渓における質量収支の研究

抄録

The Yukikabe perennial snow patch with a volume of 2×10⁵ m³ at most is located at lat. 43.6°N and long. 142.9°E, lying on the east slope, 1720 to 1760 meters in elevation, at the Takanegahara Plateau in the Daisetsu Mountains. Twenty-five longitudinal cross sections of Yukikabe were drawn from measurements which were carried out during the summer only from 1964 to 1972. If one assumes that the density of Yukikabe snow patch is constant, the mass balance will be expressed in terms of the thickness. As Yukikabe is divided by different mass balance scheme into upper and lower parts with an angle of about 15° and 40° respectively, one point on both parts was adopted as the representative station in considering the mass balance. Accumulation and ablation were deduced from the changes in the thickness of snow patch at these two representative points. About 20 meters of summer ablation was observed at both parts. They can estimate the minimum thickness at the end of summer season from limited data of thickness, for there is a good correlation between the rate of ablation and the accumulated air temperatures (degree·days) at Asahikawa Weather Station about 100 km apart, assuming a lapse rate of 0.6°C/100m. The estimated net balances are verified by comparison with the results obtained on the surface of Yukikabe in late summer. The thickness of the upper part remains 26 meters during the winter season, while the thickness of the lower part varies from 15 to 30 meters depending on the amount of drifting snow from the Takanegahara Plateau. The square of the maximum thickness of the lower part is found to be closely related to the sum of products, P times V³, where P (mm) is the mean precipitation at four meteorological stations near the Daisetsu Mountains and V (m/s) is the daily mean wind velocity at 800 mb at three stations during the winter. Thus, the net balance of Yukikabe can be approximated by only the meteorological data at observatories.