Spatial and Temporal Variations of Frozen Ground and Snow Cover in the Eastern Part of the Tibetan Plateau
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概要
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The observations of frost depth and snow water equivalent were carried out at Lhasa, Rikeze and Nagqu in the eastern part of the Tibetan Plateau from July 1993 to March 1999. Also, the routine data at the ten meteorological stations in the same part was analyzed, which covers the observation period. Al1 the stations are located in the seasonally frozen ground region. The main results are as follows : The development of seasonally flozen ground was most remarkable at Nagqu, where the maximum frost depth was 160-200 cm At Nagqu, the frost penetration began in October and continued until the middle of March. During the frost penetration, except in the midwintor, the soil layer near the surface froze in the night and melted in the daytime. At the thawing stage from April to May, the frozen ground melted from the surface and the frozen soil layer left undergronnd becam thin. The efficiency of frost perletration, α under certain temperature conditions tends to increase with the altitude and the precipitation in the preceding autum, but α is not iufluenced by the snow cover. Exceptionally, α is large at Lingzi and Qamdo in spite of their low altitudes. This may be ascribed to the less solar radiation at these stations than other stations, which enhances the frost penetration The maximum front depth increases with the altitude except for Llngzi and Qamdo. The days of snow cover increases with the latitude, but long lasting snow cover is not usual. At Nagqu, where the days of snow cover is the second largest among the ten stations, the maximum snow water equivalent was 20 mm, the maximum snow depth was 9cm and the mean snow density was about 0.2 g cm^3. Inter-annual variation of the days of snow cover at Nagqu is almost similar to that at, Sogxian The localized negative correlation between the winter air temperature anomaly and the days of snow cover was found at Nagqu and Sogxian in the winter of 9798, suggesting the albedo effect of snow cover. The correlation is positive between the precipitation in summer and the days of snow cover at Sogxian in the preceding winter, which apparently corresponds to the snow-hydrological effect. The warm (cold) winter tends to follow the wet (dry) summer with much (little) precipitation respectively. But the relationship between air temperature and precipitation in the summer is not clear.
- 社団法人日本気象学会の論文
- 2001-03-25