Characteristic analysis of cloud-to-ground lightning activity during hailstorm process with three hail falling events

The characteristics of cloud-to-ground (CG) lightning activity of hailstorms are an important issue. Based on the CG lightning data and wind fields retrieved by three groups of dual-Doppler radar, the characteristics of CG lightning activity in a hailstorm process that included three hail events and their relationship with hailstorm dynamics and microphysical conditions are analyzed and discussed. The results reveal that: (1) Three consecutive hail events occurred during the whole hailstorm process, accompanied with three peaks of CG lightning activity, and the CG lightning flash rate increased rapidly prior to hail falling. After the hail began, the CG lightning flash rate decreased rapidly; (2) During the whole hailstorm process, the vertical velocity at 0℃ and −20℃ levels corresponding to CG lightning position were concentrated within the ranges −2—2 m/s and −10—10 m/s, respectively. However, the CG lightning positions during the three hail periods respectively corresponded to the strong subsidence airflow zone nearby, the boundary area between strong rising and sinking airflow zone and weak subsidence airflow zone at −20℃ level; (3) The three radar echo parameters, i.e., the maximum reflectivity of the hailstorm Z_max, the maximum reflectivity at −20℃ level Z_{max_ −20℃}, the grid numbers of greater than 40 dBz at −20℃ level \rmSum_(Z_-20\text℃\text＞40\;\rmdBz) , had the same trend as the CG lightning flash rate, and their correlation coefficients are 0.64, 0.64 and 0.76, respectively. The two vertical velocity parameters, i.e., the absolute value of maximum vertical velocity at −20℃ level corresponding to CG lightning position |W|_{max −20℃} and the volume number of the vertical velocity absolute value greater than 5m/s above −20℃ level |V|_{5 m/s ↑−20℃}, are proportional to the CG lightning flash rate and their correlation coefficients are 0.72 and 0.65 respectively. The maximum values of parameters of the stage corresponded to the CG lightning flash rate maximum value of the stage. Considering the dynamic and microphysical effects, the precipitation ice mass flux F has the most significant correlation with the CG lightning flash rate, and their correlation coefficient is 0.85. The CG lightning flash rate was low in the second hail stage, when the hailstorm developed most rigorously. It is inferred that the characteristics of charge structure under strong dynamic process is not conducive to the occurrence of the CG lightning. However, the dynamic process played a positive dominant role during the whole hailstorm process. The updraft changed ahead of the ice crystal mass and lightning rate changes, and affected the radar echo changes.