A CASE STUDY OF LOW LEVEL SHEAR LINE OVER YANGTZE-HWIA VALLEY IN CHINA

During summer very often there is a heavy-rain bearing west-east shear line in the lower troposphere over Yangtze-Hwai valley. To the north of the shear line, the wind is predominantly from east or northeast, and to the south from the west or southwest. Its appearance is most evident on 850 and 700 mb surface. In this paper a case study of this type of shear line is made. It is shown that the dynamical and thermal effects of Tibet plateau is the one of the important factors for its formation.The analysis of the three dimensional wind field in the region of the shear line, shows that the pattern of the vertical circulation has an important influence on the horizontal distribution of temperature and humidity near the shear line, thus it is closely related to the genesis and development of the. low level frontal zone. Moreover, several problems concerning the synoptic meteorology in subtropics over Far East during summer are discussed. They include:the influence of vertical circulation on the frontal zone;the process of the transformation of a polar front into an equatorial front and the nature of the some weather systems in subtropical region of China in summer. The author has offered several explanations about these characteristics.