THE CLIMATIC AND SYNOPTICAL STUDY ABOUT THE RELATION BETWEEN THE QINGHAI-XIZANG HIGH PRESSURE ON THE 100MB SURFACE AND THE FLOOD AND DROUGHT IN EAST CHINA IN SUMMER
Luo Siwei Qian Zhengan Wang Qianqian ( Lanzhou Institute of Plateau Atmospheric Physics, Academia Sinica )
According to the analysis of 13 years data, it is shown that there are close relations between the ridge and center positions of Qinghai-Xizang high pressure on 100mb surface and the large scale distribution of floods and droughts in East China in summer. 1 The ridge position of Qinghai-Xizang high pressure on 100mb surface, especially at 120°E, is closely related with the periods of Mei-yii and mid-dle summer drought. In the period of Mei-yti the ridge position at 120°E is located in the 26°-32°N and in north of 33°N while in the period of mi-ddle summer drought. 2 The center of Qinghai-Xizang high pressure always occurs over the Plateau. It may be related to the heatimg effect of the Plateau in summ-er. The center and ridge positions of Qinghai-Xizang high pressure on 100 mb surface and the direction of ridge at 90°120° are also closely related to the drought and flood in East China. 3 There are three cirulation patterns i.e. east pattern, west pattern and zonal ( transitional ) pat tern. In the periods of east and zonal circula-tion patterns the droughts occur at the middle and lower reaches of the Yangtze River, East Sichuan and Guizhou provinces and the floods occur at the West Sichuan and North China. On the contrary, the west circula-tion pattern brings rainy weather to the middle and lower reaches of Ya-ngtze River, East Sichuan and Guizhou provinces, resulting in floods, but no raining weather ( drought ) occurs at the West Sichuan province.