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炭酸ガスなどの温室効果ガスの増加によって,地球の気候が温暖化するのではないかという「地球温暖化」問題には,気候システムにおける未解明な機構による大きな不確定性が伴っている.ここでは,その主要なひとつである雪氷圏に起因する不確定性に関する現在の認識と,今後の課題についてのべる.

Through the monsoon period of 1976, precipitation phenomena were observed at temporary stations around peaks and ridges of high altitude (5000-5500 m) in Shorong and Khumbu Himal, in addition to the observations made at Lhajung station (4420 m) in the Khumbu region. Through these observations, it was found that the amounts of precipitation at these two stations is 4 or 5 times larger than that at Lhajung. While day to day convective precipitation contributes the major part of the total amount at Shorong and Glacier EB 050 (E9) stations, a few rainy days of large amount of precipitation account for most of the contribution at Lhajung station. It was also found that the statistical features of precipitation as a function of time of day are systematically different among these three stations. Along the slope to Glacier EB 050 (E9) in Khumbu Himal, the amount of precipitation gradually increases with increase of altitude. However, along the slope to Glacier AX 030 in Shorong Himal, the amount is almost uniformly distributed from 4000 m up to the terminus of the glacier (5200 m).

Air temperature over two regions of the Nepal Himalayas (Shorong-Khumbu Himal and from Langtang Himal through the Indian Plain) were measured by thermistor and psychrometer set up on a Pilatus Turbo Porter aircraft. The results suggest that the air temperature field over the Himalayas is affected by high altitude orography and surface conditions.

Seasonal weather variations in Khumbu Himal are described on the basis of two full years of data (April 1973 to March 1975) at Lhajung station (4420 m). The data used are mainly the daily record of cloud, precipitation and moisture content, and the 500 mb weather charts. It is suggested that each stage of seasonal weather variation in the high-altitude Himalayas in Nepal is mainly affected by : i) The Tibetan High in the monsoon season and the subtropical jet stream in the other seasons. ii) The moisture supply to this region from the Indian Ocean. There are also strong year to year variations depending on the strength of the subtropical jet stream and the Tibetan High.

Spectral analysis was performed on records of the daily precipitation during the monsoon season of 1973 at stations in the Nepal Himalaya. Through power spectral analysis on the data at 12 stations and also on the areal averaged data (east, central and west Nepal), a predominant periodicity of around 10 days and secondary periodicity of about 5 days are found. Through cross-spectral analysis between these data, the periodicity around 10 days is found to be correlated with large-scale disturbances causing precipitation simultaneously in all of Nepal, and the periodicity of about 5 days seems to be associated with monsoon lows moving westward along the monsoon trough in northern India. The periodicity of around 10 days also seems to be related to the oscillation of the Tibetan High and or level of activity of the monsoon regime over the Indo-Tibetan region.

In the post-monsoon period, surface temperature at Ganesh and Langtang Himal areas were measured by an infrared (IR) radiometer on a Pilatus Turbo Porter aircraft. The results show the extremely high temperatures at bare and less vegetated surfaces of the Himalayan highland (over 4, 000 m) due to heating by strong solar radiation, and also large temperature differences between sunlit and shaded surfaces.

During the winter of 1975, two core drillings of lake sediments were carried out in Tsola-Tso, Khumbu Himal and two cores, 1.99 and 3.07 m long, were obtained. Preliminary observations of the core lithofacies were made and are summarized as follows. 1) The lithofacies show the alternation of fine and coarse materials. 2) The thickness of each layer varies from 0.5 to 15 cm. 3) The core is classified into three part from the lithofacies, that is, top to 90 cm depth, 90 to 150 cm depth and below 150 cm depth.