The favorable factors that affect the initiation of intracloud (IC) lightning and cloud‐to‐ground (CG) flashes are investigated by using a fine resolution two‐dimensional lightning model. Simulation results indicate that potential at initiation point is a key to decide whether downward leader reaches ground. The absolute values of initiation potential of CG flashes are greater than 30 MV, while the absolute values of initiation potential of IC lightning are basically less than 30 MV. Since potential field is determined by space charge distributions, polarities and types of lightning discharges are also dependent on relative locations and magnitudes of positive and negative charge zones near initiation points. In general, dipoles (positive charge above negative) initiate normal IC lightning and positive CG flashes and inverted dipoles are associated with inverted IC lightning and negative CG flashes. The magnitude of upper charge near initiation point is generally larger than that of lower charge when CG flashes occur, and the two are comparable when IC lightning occur. For CG flashes, the magnitude of lower charge near initiation points should be enough for initiation breakdown, but not so strong that the lower potential well prevents propagation to ground. In addition, CG flashes are initiated within various special charge distributions, only if the reference potentials at initiation point are far away from 0 MV.

The effect of aerosols on lightning has been examined in many studies, but its mechanisms are complex and far from understood. This study investigated the influence of aerosols on cloud-to-ground (CG) lightning during both afternoon (12:00–18:00 Beijing Time) and night (23:00–05:00 Beijing Time) in the Sichuan Basin by analysing 9-year datasets of CG lightning, aerosol loading, dynamic-thermodynamic, and cloud-related data from ground-based measurements, satellite, and model reanalysis to understand the difference in the influences of aerosols under conditions with and without solar radiation. The relationship between lightning and aerosol optical depth (AOD) is nonlinear in the afternoon and at night with a turning point at AOD ≅ 0.3. When AOD is less than 0.3, increasing AOD will lead to an increase in lightning flashes both in the afternoon and at night. When the AOD exceeds 0.3, the increase of AOD will reduce the lightning flashes in the afternoon but have no obvious effect on the lightning flashes at night. The different relationship between aerosol loading and lightning flashes in the afternoon and at night after AOD exceeds 0.3 is related to the changes in solar radiation in these two periods. In the afternoon, excessive aerosols reduce the solar radiation reaching the ground through its direct and indirect radiative effects, resulting in the decrease of the surface temperature, increasing atmospheric stability, inhibiting convection, and thus reducing lightning. At night, due to the absence of solar radiation, the influence of aerosols on surface temperature is weakened; thus, the inhibition of aerosols on lightning activity is weakened.

Numerical simulations are performed to investigate the effect of varying CCN (cloud condensation nuclei) concentration on dynamic, microphysics, electrification, and charge structure in weak, moderate, and severe thunderstorms. The results show that the response of electrification to the increase of CCN concentration is a nonlinear relationship in different types of thunderclouds. The increase in CCN concentration leads to a significant enhancement of updraft in the weak thunderclouds, while the high CCN concentration in moderate and severe thunderclouds leads to a slight reduction in maximum updraft speed. The increase of the convection promotes the lift of more small cloud droplets, which leads to a faster and stronger production of ice crystals. The production of graupel is insensitive to the CCN concentration. The content of graupel increases from low CCN concentration to moderate CCN concentration, and slightly decreases at high CCN concentration, which arises from the profound enhancement of small ice crystals production. When the intensity of thundercloud increases, the reduction of graupel production will arise in advance as the CCN concentration increases. Charge production tends to increase as the aerosol concentration rises from low to high in weak and moderate thundercloud cases. However, the magnitude of charging rates in the severe thundercloud cases keeps roughly stable under the high CCN concentration condition, which can be attributed to the profound reduction of graupel content. The charge structure in the weak thundercloud at low CCN concentrations keeps as a dipole, while the weak thunderclouds in the other cases (the CCN concentration above 100 cm⁻³) change from a dipole charge structure to a tripole charge structure, and finally disappear with a dipole. In cases of moderate and severe intensity thunderclouds, the charge structure depicts a relatively complex structure that includes a multilayer charge region.

The effect of aerosols on lightning has been noted in many studies, but much less is known about the long-term impacts in air-polluted urban areas of China. In this paper, 9-year data sets of cloud-to-ground (CG) lightning, aerosol optical depth (AOD), convective available potential energy (CAPE), and surface relative humidity (SRH) from ground-based observation and model reanalysis are analyzed over three air-polluted urban areas of China. Decreasing trends are found in the interannual variations of CG lightning density (unit: flashes km⁻²day⁻¹) and total AOD over the three study regions during the study period. An apparent enhancement in CG lightning density is found under conditions with high AOD on the seasonal cycles over the three study regions. The joint effects of total AOD and thermodynamic factors (CAPE and SRH) on CG lightning density and the percentage of positive CG flashes (+CG flashes/total CG flashes × 100; PPCG; unit: %) are further analyzed. Results show that CG lighting density is higher under conditions with high total AOD, while PPCG is lower under conditions with low total AOD. CG lightning density is more sensitive to CAPE under conditions with high total AOD.