The Feature of Raindrop Collision Process Revealed from Ground-Based Disdrometer and Dual-Polarimetric Radar

The significant variation in drop size distribution (DSD) is primarily due to various microphysical processes. In contrast to previous classification methods based on weather system characteristics, the new classification method based on theoretical foundations and DSD observations to evaluate warm rain collision processes characteristics. Results showed that the collision rate (CR) and the probability of collision outcome (Prcollision) could effectively classify DSD features and predict the fingerprint of collision process (highest slope and lowest slope, HS & LS). Since the DSD of the entire weather system can’t be completely observed, the DSD is converted into different moments, Mp, and compared with its collision characteristics. The results show that in addition to the good linear relationship between CR and M3, adding more different moments can distinguish the collision process-oriented DSD.
Although Prcollision is not easily represented by a specific Mp, its coefficient Cp in the power-law relationship between different moments can be compared. When the Cp of low (high) moments increases over time, the collision breakup (coalescence) process becomes dominant.
Long-term statistical results also indicated that both collision processes were most prominent in Taiwan's summer (during afternoon convection) compared to other weather systems. Therefore, a case study of afternoon convection during the TAHOPE/PRECIP experiment in 2022 was conducted to better understand the method (based on temporal variation) and compare it with the collision process classification proposed by Kumjian and Part (2014) (based on vertical variation). The results showed that collision fragmentation was also likely to occur simultaneously with collision coalescence.