# A Process-Oriented Method for Tracking Rainstorms with a Time-Series of Raster Datasets
## 4 Results and Discussion
### Dynamic Characteristics of a Given Rainstorm Process  
The study area is mainland China, and the real precipitation dataset comes from the Integrated Multi-satellite Retrievals for Global Precipitation Mission (GPM/IMERG) final precipitation products, version 05B, which provides global precipitation datasets with a spatial resolution of \(0.1\times 0.1^{\circ}\) and a temporal resolution of 0.5 h [28]. This dataset has been evaluated and widely used in China [29; 30; 31]. The time span of the dataset used is from March 2014 to December 2017, and the spatial range of the dataset covered in this paper is shown in Figure 10.  
Based on our analysis and existing knowledge, PoAIR chooses 8 neighborhoods [9; 32] to transform the spatially-connected grid cells to spatial rainstorm objects, an area-overlapping threshold of 0.6 [8; 12], and a maximum research radius of 58 km to link the rainstorm sequences [26]. There is a total of 300,201 rainstorm processes in the dataset. Among them, the rainstorms which occurred during the period of 18-21 July 2016, involved a complicated rainstorm process, which included 373 sequences and 2560 objects, and 254 merging, 263 splitting, and 150 merging-splitting behaviors. Figure 11  
Figure 10: Research area and remote sensing dataset coverage.  
shows the rainstorm process, and mainly displays the key time snapshots when splitting, merging, or merging-splitting behaviors occur, or when local stations publish altering information.  
The rainstorm processes shown in Figure 11 originated in Shaanxi, Hubei, and Hunan provinces. As time went by, the rainstorms gradually moved to Northeast China with splitting, merging, and merging-splitting behaviors, and eventually terminated in Liaoning Province. At 01:00 on July 20, rainstorm objects originated in Shaanxi Province, and those in Hunan and Hubei provinces merged in the middle of Henan Province and then moved Northeast. At 02:30 on July 20, this merged rainstorm object split into two parts, one of which continued to weaken and terminated in Henan Province at 18:00 on July 20; the other part kept on moving Northeast and then split into two parts at 00:30 on July 20. Meanwhile, other rainstorm objects affecting Beijing, Tianjin, and Hebei provinces continued to strengthen and moved towards Liaoning Province. At 09:00 on July 21, this rainstorm process split again, and each part continued to weaken. Finally, it terminated in Liaoning Province at 19:30 on July 21. As can also be seen in Figure 11, this rainstorm process closely coincides in space and time with the rainstorm warning information issued by multiple meteorological stations.  
Figure 12 shows one of the basic rainstorm sequences which occurred between 22:00 on July 20 -01:00 on July 21, including seven rainstorm objects. The sequence only had developing behaviors, and its rainstorm objects had a similar movement direction and similar geometrical and thematic features, as shown in Table 5. This similarity proves that the PoAIR algorithm produces desired results.  
Figure 11: _Cont._  
Figure 11: The dynamic characteristics of rainstorm processes over mainland China between 18–21 July 2016. The background is rainfall from GPM/IMERG products, the black lines denote rainstorm objects, and the text balloons present spatial and temporal information of rainstorm warnings from stations.