Wang Dehui, Zhang Peiyuan
During the period of a field investigation in 1958-1959, 6 observational sites were set up along the Urumqi valley to carry out climatological observations.Analysis of results is as follows:(1) The temperature lapse rate on the northern slope of Tianshan in summer is about 0.65℃/100 m and strong inversion appears in winter. Tianshan is a humid belt lying across the semi-arid area of Xinjiang. In summer, the mountainous area has more precipitation than outside the mountains, while in winter, vice versa. The precipitation is in solid for the whole year at an altitude higher than 3,000 m. However,the distribution of evaporation over the mountainous area and the outside is contrary to that of the precipitation.(2) When cold front penetrates into the north of Tianshan, fog is often seen climbing upward from the basin along the valley and then precipitation occurs. In summer, after snowfall, glacier stops melting, and one or two days later, surface runoff is formed in front of the glacier, becoming larger and larger until the next snowfall. Under the control of high pressure ridge behind the groove in the mid-troposphere, whole day clear will last for one or two days, and then showery rain will be at noon.(3) According to investigation, two maximum precipitation belts were discovered in the altitudes of 2,000m and 3,500 m.(4) Under the control of high pressure ridge in mid-troposphere, the contribution of the local convection to showery rain in the mountainous area is not large. When the cold air invasion is evident,the amount of precipitation rises with height. When the westerly in the upper air is a little fluctuated, the main contribution to the total amount of precipitation belongs to the local effects of middle-sized landform.(5) Though the site of Tianshan Station(3,480)lies in the southwest of Urumqi, but when the cold air invades from the north, the Tianshan Station often begins to snow 4 or 5 hours before Urumqi, showing the importance of topographic up lifting of precipitation frontal warm air in the process of precipitation.(6) Above 3,000 m,the southern slope is not warmer than the northern slope.
