Three kinds of satellite infrared imagery from 2001 to 2009

namely

GMS-5

FY-2B

and FY-2C

were used to study the characteristics of convective cloud mergers in summer severe weather in the Huaihe and Yangtze River basin. In the 35 heavy rain and 43 hailstorm cases

the occurrence probabilities of cloud merger were 94% and 65%

respectively. The average cloud merging times were 11.6 and 1.9. In addition

five statistic factors

namely

distance of two clouds （Dis）

ratio of two cloud areas （Ar）

minimum of two cloud top bright temperature clouds （Tmin）

difference of two cloud top lowest bright temperature （dTmin）

and change of Tmin （ΔTmin）

were calculated and compared in the cases of hailstorm and heavy rain. Three similar points were found for the two kinds of severe weather. The quantities of the four factors comprised the main differences of the merging process in the two kinds of severe weather. Based on the combination of Tmin and dTmin

the cloud top temperature conditions and the statistic probabilities of occurrence with different Ar were analyzed. Finally

three indicators for severe weather forecasting were revealed with Dis and Ar factors.