Quantitative Analysis of the Glacial Effect on Precipitation of Glacier No. 1 at the Headwaters of the Urumqi River, Tianshan Mountains

Generally speaking. precipitation on mountain glaciers is an intergrated result of weather system. terrain and specific property of the surface. The first two factors are dominant but the last one is quite important in some circumstances. In this paper, the Glacier No.1 at the headwaters of the Urumqi River, Tianshan Mountains. is selected to be a representative glacier and the factors producing precipitation on the glacial zone ale systematically analyzed. The effect of the glacier surface on precipitation is elaborated and the contribution rate of the Glacier No. 1 to the precipitation is calculated. The influence of glacier on precipitation due to its special surface is brought about through the cooling effect and its consequent phenomena: temperature jump, temperature reverse. glacier wind. coagulation height drop and horizontal precipitation. Owing to the special surface of snow and ice, the coagulation height above the Glacier No. 1 is about 146 m lower than that of Daxigou Meteorological Station about 1 000 m far away in July. The mean precipitation gradient of the Urumqi River basin (above 2 130 m) is 10. 11 mm / 100 m. different to the glacial zone, about 23 mm / 100 m. The contribution of the Glacier No.1 to precipitation is changing with height. At the tongue of the glacier only 1% of precipitation is contributed by glacier and the percentage increases gradually with height. At the firn basin (about 4 030 m) the contribution achieves the maximum. 7.55% of annual precipitation, and then decreases with height. The changing feature of air mass causes this phenomenon. When the air mass moves from the tongue of a glacier to the firn basin, its feature gradually changes and its mass loses through precipitation. When it arrives the firn basin its feature changes greatly and loses most of its mass. So when it moves up no more mass could lose and the contribution of glacier will decrease. In general, about 5.60% of the annual precipitation can be attributed to the glacier because of its special surface.