Distribution and Spatiotemporal Variations of CloudtoGround Lightning ov er the Yangtze River Basin and Adjacent Areas During the Summer of 2007
Based on the June-August 2007 cloudtoground (CG) lightning dataset provided by the Meteorological Observation Center of China Meteorological Administration , the distribution and spatiotemporal variations of CG lightning over the Yangtze Riv er Basin and adjacent areas during the summer of 2007 are analyzed and compared wi th the thunderstorm distribution, the lightning distribution from loworbit sat ellites and with the deep convection distribution denoted by TBB≤-52°C. The re sults show that the four distributions are, to some extent, consistent with each other. By comparing the 2007 CG lightning distribution with the lightning distr ibution from the loworbit satellites, the CG lightning was more active over the Ya ngtzeHuaihe River Basin, Sichuan, Chongqing, the Northwest Zhejiang Province, t he middle of the Wuyi Mountains during the summer of 2007. In addition, the CG li ghtning was more active in July and August than in June, and the location of act ive areas is farther north, however, the positive CG lightning is the most active in July. It shows that the mesoscale convective systems occurred more often in July 2007. Diurnal variations of CG lightning were different over different area s. Over the Sichuan Basin and the YangtzeHuaihe River Basin, the diurnal varia tions of CG lightning had multiple active peaks, but there was only one active pe riod of CG lightning all day long over ZhejiangJiangxiFujian area. The CG light ning was often more active in the afternoon over the YangtzeHuaihe River Basin and ZhejiangJiangxiFujian area, but it had an obvious nocturnal feature over the Sichuan Basin. In the Southwest Sichuan Basin, the CG lightning obviously pro pagated eastwards and northwards. It is also found that there is a marked differe nce between the diurnal variations of positive CG lightning and negative CG ligh tning over the western Sichuan Plateau, the middle YunnanGuizhou Plateau and t he coastal areas in Zhejiang. By comparing the diurnal variations of negative CG lightning with the positive CG lightning and the frequency of TBB≤-52℃ from the F Y-2C satellite, the active period of negative CG lightning was often ahead of t hat of positive CG lightning and the active period of positive CG lightning in t hose areas was ahead of the frequency of TBB≤-52℃. It implies that the diurnal variations of negative CG lightning reflected the diurnal variations of initial convection, and positive CG lightning and the frequency of TBB≤-52℃ reflected the diurnal variations of mature and dissipating convections.