Distribution And Spatiotemporal Variations Of Mesoscale Convective Systems Over China And Its Vicinity During The Summer Of 2007

The persisting rainstorms, extremely heavy precipitation and severe convective events resulted in tremendous damage in economy and severe personnel casualty during the summer of 2007. Based on the 2007 June-August hourly FY-2C infrared TBB, NCEP reanalysis, the distribution and spatiotemporal variations of mesoscale convective systems (MCSs) over China and its vicinity during the summer of 2007 are analyzed, the mesoscale convective systems are investigated over the area of 100～130°E,25～38°N, and the development of two MCSs causing local heavy rainstorm is given. Main results are as follows:(1) There was pentad variation of the MCSs over China during the summer of 2007, which is associated with the pentad variation of the large-scale circulation. The results show that the MCSs had two active periods over the Tibetan Plateau, the Yun-Gui Plateau, Chuan-Xi Plateau, Sichuan Basin and the Yangtze-Huaihe River Basin, and particularly the MCSs during the second period resulted in extremely heavy precipitation and severe convective events during the summer of 2007.The statistical characteristics of TBB less than -52℃show that there were four active MCS regions over China during the summer of 2007,which were South China, the Tibetan Plateau, the Yun-Gui Plateau, the area of Sichuan Province and Chongqing City, and the Changjiang-Huaihe River Basin. The diurnal variation of the MCSs over South China and the Tibetan Plateau is significant.(2) The four active MCSs regions in 100¹30°E and 25³8°N were located in the west of Sichuan Basin, Chongqing City, the area from Yun-Gui Plateau to Dong-Ting lake and the Huaihe River Basin.The MCSs can be classified as three kinds according to their time scale. The life cycle of MCSs which is great than twelve hours is defined as the first kind. The second one is the MCSs lasting about six to eleven hours and the last one is the MCSs whose life cycle is about three to five hours. These three kinds of MCSs had different geographical distributions, trigger mechanism, and diurnal variations. The diurnal variations of the genesis, the maximum extent and the number are also different over different underlying surfaces.(3) The persisting rainfall in Huaihe River Basin in 2007 can be divided into three stages, and most of the precipitation occurs in the fist stage. There were obvious differences of diurnal variations at different stages, and the total amount of the MCSs which had impact on the persisting rainfall in the Huaihe River Basin is 125. Most of these MCSs occurred and disappeared in the Huaihe River Basin and the MCSs moving from Tibetan Plateau can not be found in this region.(4) The heavy rain event occurred in Nanjing City from 7 to 9 July 2007 was caused by two M_αCSs in the Meiyu front, and these two M_αCSs originated from several smaller-scale MCSs. The heavy rain event occurred in Chongqing City from 17^th to 18^th July 2007 was also caused by two M_αCSs, but one M_αCS moved eastward and developed, and the other formed from several smaller-scale MCSs. A 38-hour duration M_αCSs developed twice and its path had a characteristic of abrupt change.