On the Characteristics and Possible Causes of A Severe Drought and Heat Wave in the Sichuan-Chongqing Region in 2006

During July to September in 2006,the Sichuan-Chongqing region of southwestern China suffered from a severe drought and heat wave,which were record-breaking in the past 50 years.This study focuses on the related characteristics and possible causes of the severe drought and heat wave.The abnormal summer climate of the Sichuan-Chongqing region directly caused by the long-term maintenance of a subtropical high pressure belt aloft in the middle and upper troposphere,whose axis was situated along 30°N.The amplifications of western Pacific subtropical high(WPSH) and Tibetan high in a wide meridional extent both contributed to the formation of such a unified subtropical high pressure belt.Specifically, the Tibetan high extended eastward,with its center still located in the Iran Plateau,giving rise to the amplification and westward extension of the WPSH.As a result,both the Tibetan high in the upper troposphere and the WPSH in the middle troposphere mer ged into one subtropical high pressure belt.Meanwhile,the mid-latitude westerlies as well as the accompanying transient disturbances shifted poleward from their climatological position,which is favorable to the maintenance of subtropical high pressure system over the Sichuan-Chongqing region.The lower tropospheric vortex originated from the eastern slope of the Tibetan Plateau,which is also called southwestern vortex and a major rain-producing weather system locally,was weaker in this summer than normal.In the tropics,the abnormal condensational latent heat releases over the western Pacific Intertropical Convergence Zone(ITCZ) and the Bay of Bengal possibly contributed to the maintenance of subtropical high pressure system over the Sichuan-Chongqing region.