Cumulus Merging in the Massive Mudslide of Zhouqu Using Meteorological Satellite Data

Heavy rainfall occurs abruptly at Zhouqu, Gansu Province from 7 August to 8 August of 2010, causing massive mudslide and brings about huge casualties. As an observational fact, it is clear that a meso-scale convective system, which is produced by several convective cells merging, brings heavy rain in local field and the massive mudslide at Zhouqu. The phenomenon of cumulus merging is analyzed using meteorological satellite data, such as FY-2D/E, NOAA-18 and FY-1D, to find out its impact on heavy rain.As NOAA-18 satellite image shows, there are several cells around the Zhouqu at 0638 UTC 7 August 2010. One and half hours later, cells are merged and forms a meso-scale system. And the meso-scale system is still developing in FY-1D satellite image.From FY-2D/E satellite images, there are five stages of cumulus merging in the whole process. First, the meso-scale convective system comes out due to the merging of multi-cells from 0700 UTC to 0800 UTC. And it is the developing and maintaining period of meso-scale convective system. The cumulus merges in 3 stages. First, a developing system merges with several nearby new generation cells at about 0930 UTC. Then a systems merges between a mature new generation system and the old convective system from 1000 UTC to 1030 UTC, the new and old systems merge from 1130 UTC to 1200 UTC. Finally, two centers of cloud with cold cloud top temperature are merged as the dissipating of convective system after 1300 UTC. As the centers have been merged, the system develops again and the cold cloud areas have increased.As a result of the merging effect, not only a large and complex convective system is produced and becomes more intensity, but also the lifetime of convective system is greatly enhanced with more convective energy.On the other hand, the mechanisms of merging in five stages could be classified as change of inner dynamical structure and collision with outer force. At the building stage of meso-scale convective system, collision with outer force is the main cause of cumulus merging. But with the development and maintain of system, inner changes of dynamical structure, such as pressure gradient force, convergence and up-down circumfluence, are the primary mechanisms for merging.