SPACE-TIME DISTRIBUTION AND PHYSICAL MECHANISMS OF AUTUMN RAINS IN WEST CHINA IN 2001

The space-time distribution features of autumn rains in West China in 2001, the related large-scale atmospheric circulation, and the main features of the weather systems are analyzed to study the physical mechanisms of autumn rains.The results show that there were more rainy days than normal in 2001, and the strong raining processes were concent rated around Sichuan Basin in September.The circulation analyses show that there was a quasistationary t rough near the Oz.Balchas, from which short waves were split one by one, moved southeastw ard, passed Tibet Plateau and reached the area near Sichuan Basin.Here the cold ai rs taken by the short waves were combined constantly with the warm and humid southeastair in the southeast side of the strong subtropical high and with the wet-warm south west air from the Bay of Bengal.The physical analyses show that there was a strong energy frontal zone between the high energy center in Tibet Plateau and the lowenergy center to the east of Sichuan Basin.So the short waves were developed strongly in the Basin. The intensity of the energy frontal zone was streng thened because the cold air from the east area entered so that the instability energy burst out, which triggered the rainstorm in Sichuan Basin.