THE BASIC FEATURES OF DISTRIBUTION OF WATER VAPOURCONTENT AND THEIR CONTROLLING FACTORS IN CHINA
Zhou Jinshang Liu Huilan (Department of Meteorology, Nanjing University)
In this paper, We have calculated average monthly values of water vapour content of air column above unit area of one square centimetre at the earth's surface and the levels of 850, 700, 500 and 600 mbs respectively. The calculation are mainly based on the meteorological data of 103 aerological stations during the period of 1960-1969 in China. The charts of average amounts of water vapour content for each of the months, i.e. January, April, July and October, and the time cross sections along latitude of 33°N, and longitudes of 90°E and 110°E are presented. The basic features of distribution and variation of water vapour content over China are briefly described as follows: 1. In general, the mean values of water vapour content are decreased northwest- ward from South China. The maximum is located near the northern Gulf, where the amount of water vapour is about 62 mm. The centers of large values of moisture are found in the Sichuan Basin and the two large lakes area. The minimum over the Tibetan Plateau is due to the high elevation of the terrain in that area. 2. The amount of water vapour content decreased rapidly as the altitude in- creased. On the average, the amount of moisture of air above unit area of one square centimetre in the layer from the surface up to 500 mb is in excess of 90% of that at the earth's surface. 3. The patterns of the months from October through April show a slight change in form and in magnitude of water vapour content. But by May, a noticeable increase of moisture over the central and eastern China begins to appear and continues through July. Therefore, July is the month with the maximum value of water vapour for China, and January (or February) is the month with the minimum amount. Excep- tions are those stations in the southern coast of China with maxima in June. As for the position of maximum longitudinal gradient of water vapour content, it moves with the transition of natural weather season. In winter, the maximum gradient locates in 20°-25°N, in Spring, 30°-35°N, and in Summer, 35°-40°N. In Autumn, it returnes to 30° -35°N. 4. Another feature is very important that there is an extensive tongue of moisture extended northeastward by east from the southern coast of China. After the appearance of the tongue of moisture in April, it is developed very strongly in June. Obviously, it is associated closely with the lower jet stream. 5. A center of moisture over Tibetan Plateau on charts of water vapour content in the layer from 600 mb up to 200 mb was found, its tongue extends eastward from terrain. This center of moisture begins to appear in June and continues through Sep- tember. August is the month of maximum amount over there. Finally, the paper discussed in details the factors, which include geographi- cal latitude, proximity of sea and land, topography, monsoon and weather regimes have significant influences on the distribution and variation of water vapour content in our investigating areas.