## 3 Results  
### Effects on the Intensity and Distribution of Precipitation  
The effect of over-seeding is presented in Weather Modification [67]. Similar results can also be found in our research. Figure 2 shows time series of domain-averaged surface precipitation rate (DPRE). It can be seen in Figure 2a that precipitation begins after t = 14 h in all nine cases. Interestingly, a slight variation of DPRE can be found with the increase of \(N_{c}\) before t = 18 h, but after then, such differences reach amplitude peak at t = 21 h. Note that the changes of DPRE are nonmonotonic with the increase of \(N_{c}\). More specifically, DPRE increases with \(N_{c}\) ranging from 50 cm\({}^{-3}\) to 3500 cm\({}^{-3}\), but decreases slightly when \(N_{c}\) ranges from 3500 cm\({}^{-3}\) to 5000 cm\({}^{-3}\).  
In order to understand model behavior over a wide range of conditions, we carried out 9 experiments. However, 5000 cm\({}^{-3}\) is more than in-situ observations in recent, which might occur in the future with much higher urban air pollution. For simplicity, here we focus on two typical conditions, one is typical continent condition case (C-case) and the other is polluted continent condition case (P-case) in Mei-Yu front. Previous observations indicated that droplet concentration is about 100-300 cm\({}^{-3}\) over continents [68]. Nevertheless, [PERSON] et al. [69] demonstrated that droplet concentration reaches 2400 cm\({}^{-3}\) in polluted clouds over the Amazon by observation. Cloud droplet concentration also reaches 1900 cm\({}^{-3}\) in northern China [70]. Therefore, droplet concentration herein is set to 250 cm\({}^{-3}\) for C-case, while 2500 cm\({}^{-3}\) for P-case due to the severe air pollution in Yangtze River basin [54,71]. A similar set was also adopted to investigate the aerosol effects on squall line in [PERSON] et al. [72].  
Figure 2: Time series of (**a**) domain-mean surface precipitation rate (mm h\({}^{-1}\)) in 9 experiments, (**b**) in C-case and P-case only, (**c**) domain-mean accumulated surface precipitation (mm) from t = 14 h to 15 h, and (**d**) domain-mean accumulated surface precipitation before t = 27 h in C-case and P-case.  
Figure 2b shows time evolution of DPRE in C-case and P-case. Note that precipitation of both cases starts after t = 14 h, but the onset of surface precipitation in C-case (P-case) is at 14:30 (14:40). Precipitation in C-case starts 10 min earlier than P-case (Figure 2c). The effect of aerosol varies in different stages of the precipitation. Before t = 18 h, Precipitation rate is slightly smaller in P-case than C-case, but larger after that, and this phenomenon continues to t = 26 h. The greatest difference is about 22% between P-case and C-case in 21-22 h. Domain-mean accumulated precipitation in the two cases is also quite different after 18:00 (see Figure 2d).  
Figure 3 compares the spatial distribution of precipitation in C-case and P-case at three different times. At t = 15 h, the two cases both show a line of precipitation parallel to the front. By t = 18 h, many meso-scale and micro-scale rain cells appear on the frontal rainbands, showing the \"core-gape\" structure [73] of Mei-Yu front precipitation, but the distribution differences of rainbands are not significant between them. At t = 21 h the differences are clear, the frontal rainband of C-case is more spread-out, while the P-case rainband is closer to the front.