The Characteristics of Raindrop Size Distribution in Two Rainstorms with Extreme Rainfall Rates in Summer in Shandong Province

The raindrop size distributions and integral parameters of convective precipitation and formation mechanism of ground Raindrop size distribution in two extreme precipitations were analyzed using data from the Thies disdrometer and the CINRADA/SA Doppler radar. The results showed that: (1) The two precipitation processes were both affected by the southwest airflow outside the subtropical high and the westerly trough with the characteristics of high temperature and high humidity, which were conducive to the production of heavy rain. (2) The relationships between parameters lgN_w, D₀ and rain intensity R of severe convective precipitation episodes (rain intensity R＞20 mmh⁻¹) revealed there was a large coefficient and a small index on 3 August 2015, whereas it was just the opposite on 26 July 2017. On 3 August, D₀ rapidly increased as R increased for the median volume diameter of the raindrop, and the slope of the fitting line was large, while lgN_w gradually decreased as R increased. Furthermore, the slope of the linear fitting line was negative. D₀ and lgN_w were both positively correlated with R on 26 July 2017; however, D₀ increased slowly as R increased, and the slope of the fitting line was small. In addition, the slope of the linear fitting line was smaller. For the raindrop concentration (N_T), the exponential function can be used to fit the N_T as R increases. On 3 August, there was a large coefficient and a small index, whereas on 26 July, it was just the opposite. (3) The average raindrop size distribution of convective precipitation with different rainfall intensities show that, on 3 August, with the increase of rain intensity (R＞50 mm h⁻¹), the concentration of small particles in diameter 1–3 mm varied slightly, while the concentration of large raindrops in diameter 3–6 mm increased significantly, and the Z–R relationship of convective precipitation had a large index (1.61). On 26 July, with the increase of rain intensity, the concentration of particles in each diameter range basically increased at the same time, and the Z–R relationship of convective precipitation had a small index (1.25). In conclusion, the precipitation on 3 August had typical size-controlled raindrop size distribution characteristics, whereas the convective precipitation on 26 July had concentration–diameter mixed control of raindrop size distribution characteristics based on the relationship between integral parameters and rain intensity and the average raindrop size distribution. (4) The normalized Gamma N_W–D₀ distributions showed that the convective precipitation in the two cases had the characteristics of the typical raindrop size distribution of continental convective precipitation. Many raindrop size distributions in the processes of 3 August showed the characteristics of ice phase and warm mixed convective precipitation, but most of the convective precipitation in the two processes had the characteristics of ice-based raindrop size distribution.