Lightning channel reactivation is intimately linked to channel decay and cutoff processes, yet the transition from a conductive plasma channel to a non-conductive state remains difficult to characterize. Due to limitations of existing observation techniques, numerical modeling is essential to elucidate the mechanisms of channel decay and reactivation. A self-sustained charge neutrality intra-cloud lightning parameterization model is used to simulate multiple intracloud lightnings in various tripolar thunderstorm charge environments. The channel cutoff threshold is systematically varied to investigate its impact on lightning development and reactivation.Simulation results indicate that lightning development is highly correlated with the channel cutoff threshold. Lower cutoff thresholds (10-3-10-2 S·m-1) produce flashes with longer durations, more complex branching, and higher reactivation initiation fields (more than 300 kV·m-1). In this regime, the channel still persists even when the channel conductivity is extremely low. Consequently, a high reactivation initiation field (more than 300 kV·m-1) is required to re-ionize the decayed channel. Under these conditions, fewer than 20 reactivation processes are observed, most of which are short attempts (less than 100 m) as the channel is nearly insulating. Specifically, the low residual conductivity impedes charge transport, thereby making re-breakdown difficult to achieve. In contrast, higher thresholds (1-10 S·m-1) lead to flashes that are shorter in duration and exhibit significantly fewer branches. Under these conditions, the channel is cut off while still maintaining significant residual conductivity, effectively serving as a primed path for subsequent discharges. Consequently, the reactivation initiation field decreases to 10-120 kV·m-1, whereas the reactivation frequency increases to several hundred events, with reactivated channel lengths often exceeding 200 m. The number of significant reactivation processes notably increases. Furthermore, increasing reactivation events along the main channel lead to a further accumulation of residual conductivity. When subsequent reactivation propagates along these existing paths, the re-breakdown electric field is lowered, which facilitates the long-distance propagation of reactivation.These results indicate that the lightning development process is intimately related to the channel cutoff threshold: Higher cutoff thresholds result in earlier channel extinction and shorter flash durations, but leave higher residual conductivity, thereby favoring reactivation. Conversely, lower thresholds prolong lightning evolution and promote spatial extension, yet the diminished residual conductivity suppresses reactivation. Frequent reactivation facilitates charge transfer and mitigates electric field enhancement, whereas limited reactivation allows for greater charge accumulation and higher field intensities. Therefore, the lightning development is regulated by the interaction between channel conductivity and reactivation processes.

This article focuses on the influence of the distance between a tall building (TB) and a short building (SB) on the lightning strike outcomes of the SB. An improved stochastic lightning model is employed to conduct the simulations. The study yields several interesting findings. When the TB and SB are in close proximity, the lightning strike probability of the SB can be affected by the TB. A protective effect from the TB on the SB is observed within a distance of approximately 350 m. However, this distance is not determined by the range of the field distortion at the corner of the SB. Although 350 m exceeds the 200 m range typically associated with field distortion, it closely aligns with the 370 m intersection point of spatial distortion fields between the TB and SB. This suggests a potential correlation between the protective distance and the spatial distortion intersection distance. Beyond 350 m, the probability of lightning strikes on the SB appears largely unaffected. Nevertheless, the TB can still alter the lightning strike paths—some lightning that would otherwise strike the SB may instead strike the ground, and vice versa. While the overall lightning strike probability remains stable, individual flash outcomes may vary. Therefore, it can be inferred that a threshold distance exists beyond which the lightning strike outcomes for the SB are entirely unaffected by the presence of the TB.

Characteristics of multi-point corona discharge have been a research hotspot in atmospheric electricity, and many studies concentrate on single-point or double-point corona discharge. However, characteristics of multi-point corona discharge are worthwhile to investigate because the presence of sharp points on the ground and their interactions. In order to study characteristics of multi-points corona discharge in thunderstorm environments, a two-dimensional time-varying corona discharge model is used to simulate the process of multi-point corona discharge, and sensitivity tests are conducted. Results show that, within a certain space, as the number of points increases, the total corona charge released by points gradually increases, and when the number of points increases to a certain level, the total corona charge remains basically unchanged. The growth will not continue as the number of points increases. When the points release corona charge, the corona current ranges from 0.84×10-5 μA to 2.24×10-5 μA.Under multi-point conditions, the relative position of the point, the distance between points, and the environmental electric field play an important role in whether the point can release corona charge, and the environmental electric field is the dominant factor. As the ambient electric field intensifies, the number of points releasing corona charges gradually rises. Under the same environmental electric field, as the distance between points increase, compared to the height of the points, each point is approximately an independent point, the interaction between points decreases, and points that can release corona charge also increase.Once points release corona charge, a suppressed electric field is generated by the corona charge at points. The suppressed electric field is influenced by the total corona charge present in the space, as well as the spatial distribution of that charge. When corona discharge reaches dynamic equilibrium, the suppressed electric field value can be calculated using the environmental electric field and the electric field distortion coefficient at the specified points. When the point distortion coefficient is unique, the suppression electric field at the point is linearly related to the environmental electric field. If the point does not release a corona charge, the suppression electric field at the point is nonlinearly related to the environmental electric field. The suppression electric field at the point is entirely generated by the corona charge released from other points. Its magnitude is influenced by the environmental electric field and the point's own distortion coefficient.

Wind energy is recognized as a clean and renewable energy source and plays a crucial role in achieving the "dual carbon" goals and facilitating the transition to a low-carbon energy system. To optimize power generation efficiency, wind turbines are typically installed in exposed areas, such as mountaintops or offshore locations, where the probability of lightning strikes is elevated and the associated damage is significant. Research on lightning strike patterns on affecting wind turbines is considered vital for enhancing lightning protection capabilities.The wind farm under observation consists of 9 wind turbines, each equipped with a 115-m towers and 99-m blades. 3-dimensional total-flash lightning mapping and synchronized waveform observations are conducted using Realtime Low-frequency Electric Field Detection Array (RT_LFEDA) at China Meteorological Administration's Field Experiment Base on Lightning Science (CMA_FEBLS). Radiation source data in terms of azimuth and elevation angles for lightning strikes on turbines are obtained with a lightning continuous interferometer (CINTF).It is shows that the mountainous wind farm exhibits an attraction effect on nearby cloud-to-ground lightning. An influence range of approximately 1.8 km is observed, within which the lightning strike density is elevated. The return-stroke density decreases from 3.7 km-2 near turbines to 1.5 km-2 outside the influence zone, with an average value of 2.53 km-2. Multiple return strokes from a single flash are observed to strike different turbines, and these strike locations correlate closely with branched paths of the initial downward leader. Subsequent discharges develop along different leader branches, leading to return strokes at spatially separated positions. Furthermore, strong and weak return strokes exhibit distinct spatial distributions: Stronger return strokes being tend to occur on turbines located at lower elevations along the periphery of the wind farm. Upward leaders are initiated from multiple wind turbines during lightning events, and their initiation is observed to take place when the downward leader approaches within 100-200 m of a turbine. Lengths of upward leaders are measured to range from 161 m to 356 m, with propagation speeds between 1.8×105 m·s-1 and 2.2×106 m·s-1, and an average speed of 1.03×106 m·s-1. The average propagation speed of connecting leaders is 1.7×106 m·s-1. Electric field waveforms of return strokes are characterized by multiple peaks due to current reflection caused by the turbine structure, with an average peak-to-peak interval of 4.66 μs. The presence of reflected signals is considered to lead to overestimation of lightning current by operational lightning location systems for strikes on wind turbines.

Channel decay and reactivation are very common discharge phenomena, which have an important influence on the type, duration, and development of lightning discharges. However, how the electrical parameters in lightning channels change during reactivation processes and how reactivation affects the development of lightning leaders are still unclear. In this study, we employed the two‐dimensional self‐sustained charge neutrality lightning model to simulate the discharge process of intracloud lightning flashes and conducted an extensive analysis of channel decay and reactivation processes. Our results suggest a close correlation between the length of reactivated channels and the distribution of channel electrical parameters, and the reactivation process has a significant influence on lightning channel development. Specifically, it is found that greater charge accumulation at the reactivation starting point and higher residual conductivity of the decayed channels can lead to longer reactivated channels. And, the reactivation initiated from the positive leader end may both promote the resumption of the extension of the positive leader branch that has stopped extending and accelerate the propagation of an advancing positive leader. Moreover, reactivation may also activate the decayed negative leader channel, facilitating the lateral generation of new branches, which is crucial for the formation of hybrid lightning, needle‐like structures, etc. The simulation results validate the previous speculations from observation studies regarding the potential influence of the reactivation process on lightning channel development and lay the foundation for the subsequent use of this model to explore the differences between the reactivation process initiated from the positive and negative leader end.

Aerosols can affect the lightning activity through radiative and microphysical effects. This study attempts to reveal the distinct impact pathways of these two effects on lightning activity. Using data of cloud-to-ground (CG) lightning, aerosol optical depth (AOD), thermodynamic, and cloud-related variables during the summer (June, July, and August) of 2010-2018 in the Sichuan Basin, we investigate the changes in the diurnal variation of lightning activity characteristics between polluted (2010-2013) and clean (2015-2018) years. Polluted years exhibit more thunderstorms during the late afternoon and early evening hours than clean years, but show no significant differences in other time periods. During all time periods, thunderstorms in polluted years are more intense, with a higher CG lightning density. Aerosols exhibit more intense radiative effect during afternoon and early evening hours in polluted years, which reduces the surface temperature, thereby enhancing atmospheric stability and inhibiting the formation of convection. The cloud liquid water and cloud ice water content in polluted years are higher, suggesting stronger aerosol microphysical effects. These results indicate that the radiative effect of aerosols primarily influences lightning activity by altering the frequency of thunderstorms, whereas the microphysical effect of aerosols predominantly affects lightning activity by modulating the intensity of thunderstorms.

Based on five years of data (2017–2021) from the China National Lightning Detection Network (CNLDN), this study compares and analyzes the temporal and spatial distribution characteristics of cloud-to-ground (CG) lightning activities in the Hengduan Mountain region and its surroundings. It explores the relationship between CG lightning occurrences and altitude, topography, and various meteorological elements. Our findings reveal a stark east–west divide: high lightning density in the Sichuan Basin and the central Yungui Plateau contrasts sharply with lower densities over the eastern Tibetan Plateau and Hengduan Mountains. This geographical dichotomy extends to the diurnal cycle, where positive cloud-to-ground (PCG) lightning activities are more prevalent in the western part of the study area, while significant nocturnal activity defines the eastern basin and plateau. The study also finds that the relationship between CG lightning activities in the four sub-regions and 2 m temperature, precipitation, convective available potential energy, and Bowen ratio (the ratio of sensible heat flux to latent heat flux) exhibits similarities. Furthermore, we show that the relationship between lightning frequency and altitude is highly region-specific, with each area displaying a unique signature reflecting its underlying topography: a normal distribution over the eastern Tibetan Plateau, a bimodal pattern in the Hengduan Mountains, a sharp low-altitude peak in the Sichuan Basin, and a complex trimodal structure on the Yungui Plateau. These distinct regional patterns highlight the intricate interplay between large-scale circulation, complex terrain, and local meteorology in modulating lightning activity.

During the process of cloud-to-ground lightning connection, the propagation of downward leader to the near-ground area can elevate the electric field at one or several points on the surface of ground tip object to the breakdown threshold of surrounding air, initiating one or more upward leaders, which are known as multiple upward leaders. The emergence of tall buildings has led to an increase in the number of observations of upward lightning strikes on different buildings or the same building. The presence of multiple upward leaders means that multiple parts of the building may be struck. Conducting simulation experiments to study the mechanism of the multiple upward leader phenomenon is of great significance for developing lightning protection. The relative velocity ratio of the downward and upward leaders may be one of the key factors in the lightning connection process. The relative speed ratio of leader propagation in random lightning connection mode cannot accurately describe the relative distance ratio of downward and upward leader propagation. Taking into account the optical observation facts and the electric field environment during thunderstorms, the background electric field module setting is improved on the basis of the existing three-dimensional random mode for multiple upward leaders. It also incorporates a relative propagation speed module for the downward negative and upward positive leaders, establishing the relative propagation speed of leaders according to their propagation distance. Applying the new model to simulate multiple upward leader phenomena triggered by a flat-roofed single building, compared with the previous version, parameters of the new model, such as flash distance and upward leader length, show better consistency with natural lightning. On this basis, the lightning connection process on the high-rise buildings in the Pearl River New Town is simulated, and the improved model can more accurately replicate the lightning occurrence patterns of complex buildings. Characteristic parameters of lightning strikes on urban building clusters are mainly determined by factors such as the shape characteristics, relative position, and relative height of each building. The distance at which lightning strikes buildings is positively correlated with their height. The probability of lightning strikes, the distance of lightning strikes, and other parameters of buildings with similar shapes in the same building group are relatively consistent during ground lightning activities. However, there are still special events that occur when a branch of the downward leader is in close spatial proximity to the building, causing the upward leader to initiate at the top of the building and connect to it.

More and more optical records have exhibited that multiple upward leaders (MULs) occur frequently on a building in the flash attachment process. An interesting issue is why a building can continue to launch upward leader (UL) after the first one appears. This phenomenon is analyzed in the present paper. Considering the influence of the leader behaviors on the ambient electric field, an improved 3-D fine-resolution lightning attachment model with MULs is established to simulate cloud-to-ground flash events with diverse leader spatial morphologies. The simulation results show that MULs may initiate almost simultaneously or with an obvious delay and the variation range of UL length is large. From this, the flash events of lightning terminating on a building are divided into four scenarios and each scenario is analyzed. It was found that the spatial location of downward leader, the length and propagation direction of the first UL and the time interval from the inception of the first UL to final jump significantly affect the electric fields at top corners of building and further affect the inception of the second UL. Based on qualitative analysis, four factors are proposed to explain why the above four scenarios happen. This research focuses on understanding the process of cloud-to-ground (CG) lightning, which can cause significant harm to society. Specifically, the study investigates the initiation of multiple upward leaders in the CG lightning process. By considering the impact of lightning leader behaviors on the surrounding electric field, the researchers develop an improved lightning attachment model. Using this model, we simulate the development of leaders and identify factors that explain why one or more leaders originate from an isolated building. The results highlight the importance of the location of the lightning, the characteristics of the first upward leader, and the timing of the lightning strike in influencing the initiation of multiple upward leaders. Future studies will explore CG lightning within groups of buildings, contributing to our understanding of this phenomenon and providing insights for protecting buildings from lightning strikes. An improved 3-D fine-resolution stochastic discharge model is developedThe spatial location of lightning, as well as the length and propagation direction of the first upward leader, has an impact on the initiation of multiple upward leadersThe time interval between the inception of the first upward leader and the final jump affects the initiation of multiple upward leaders

利用三维高分辨率的闪电随机发展模式,在保证模拟域内的两个建筑物长度、宽度和初始电场环境等基本参数不变的前提下,通过改变模拟域近地面两建筑物的相对高度、相对距离、相对方位3种建筑物相对参数来研究建筑物对周围低矮环境的落雷点(即上行先导的始发点,下同)的影响.系统阐述了不同情况下的高建筑物对于周围低矮环境的雷击保护效应.结果表明:1)固定高建筑物的高度,不断增加矮建筑物的高度,在一定高度比内高建筑物对近距离内低矮建筑物具有明显的雷击保护效应,随着两建筑物的高度不断接近(高度比越来越小)保护效应逐渐减弱,当高矮建筑物的高度比下降到小于1:0.80之后,高建筑物失去保护能力;2)高建筑物对地面在近距离一定范围内存在雷击保护效应,且具有明显的临界保护距离.当高矮建筑物之间的间距扩大到大于300 m之后,高建筑失去物对矮建筑物的保护能力;3)建筑物之间的相对方位对地面落雷点的分布影响不大.最后,笔者采用多元线性回归的方法定量的给出了建筑物之间的相对高度、相对间距对高建筑物的保护效率的影响的概率公式,经检验,具有较强的线性相关关系.

Based on the detection data of the Guangdong-Hong Kong-Macau lightning location system from 2013 to 2022, this paper analyzes the characteristics of lightning strikes in an offshore wind turbine cluster (WTC) in Guangdong. This is the first time to quantify the lightning strikes difference between the inner and outer wind turbines (WTs) and discuss the impact mechanisms of WTCs on the characteristics of lightning strikes by the simulation results of electric potential distribution. The observation results show that the stroke density, cloud-to-ground (CG) flash density, and average peak current within the affected area increase by 10.1%, 11%, and 5.1%, respectively, but the lightning multiplicity changes little. The inner and outer WTs show different characteristics of lightning strikes. The stroke density, lightning multiplicity, and average peak current in the area of outer WTs increase by 21%, 4.1%, and 6.8%, respectively, while in the area of inner WTs decrease by 20.2%, 19%, and 3.9%, respectively. The CG flash density in the area of outer WTs increases by 16.1% but changes little in the area of inner WTs. The simulation results show there is a significant difference in the electric potential distribution between the inner and outer WTs: the distortion effect of the outer WTs on spatial electric potential is stronger than that of the inner WTs at a greater height, but the difference is not obvious at a lower height. Such a difference in electric potential distribution leads to different characteristics of lightning strikes between the inner and outer WTs.

This work is conducted based on an existing two-dimensional convective cloud model to investigate the role of ice nuclei in dynamic, microphysical, electrification, and charge structure in thunderstorm clouds by changing the concentration of ice nuclei. The results show that thunderstorm clouds develop ahead of time as ice nuclei increase and both updraft and downdraft velocities decrease. A high concentration of ice nuclei enhances the heterogeneous nucleation process. In the high-temperature region, a large number of ice crystals form while the homogeneous nucleation process is inhibited. Therefore, the overall content of ice crystals decreases, resulting in a decrease in graupel content in the lowtemperature region and a decrease in graupel size in the high-temperature region. Therefore, the positive non-inductive electrification rate decreases while the negative non-inductive electrification rate increases. The time for the polarity of charge carried by high-temperature ice crystals to change from negative to positive is advanced as the liquid water content gradually decreases with increasing ice nuclei concentration. The extreme value of the inductive electrification rate gradually decreases during the process of inductive electrification due to the decrease in graupel particle size and the rapid consumption of cloud droplets. Because the ice crystals are preferentially generated in the high-temperature region and are negatively charged, the space charge structure of thunderstorm clouds with different ice nuclei concentrations presents a negative dipole charge structure at the initial stage of thunderstorm cloud development. With an increase in ice nuclei concentration, the space charge structure changes from three polarities to a complex four-order structure during the thunderstorm’ s growing period. In the dissipation stage of a thunderstorm cloud, different cases show dipole charge structures, and the charge density decreases with the increased concentration of ice nuclei.

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.

Atmospheric electricity is composed of a series of electric phenomena in the atmosphere. Significant advances in atmospheric electricity research conducted in China have been achieved in recent years. In this paper, the research progress on atmospheric electricity achieved in China during 2019–22 is reviewed focusing on the following aspects: (1) lightning detection and location techniques, (2) thunderstorm electricity, (3) lightning forecasting methods and techniques, (4) physical processes of lightning discharge, (5) high energy emissions and effects of thunderstorms on the upper atmosphere, and (6) the effect of aerosol on lightning.

Tall buildings distort the electric field of the surrounding environment, resulting in a relatively strong electric field at top corners, which affects the lightning strike process, and the protection effect that short buildings receive from tall buildings varies with the distance between them. A three-dimensional fine-resolution lightning attachment model with multiple upward leaders (LAMM) is used to simulate protection effect of a tall building and a short building with different height and distance, with an isolated building set as a control group. Experimental results show that when there is a tall building with a short building in the space and two buildings are close to each other, the distortion range of the tall building almost completely contains the distortion range of the short building, the development of downward leader is completely affected by the tall building, and the shielding effect of the tall building on the short building is significant. With the increase of the building distance, the shielding effect of the tall building on the short building decreases exponentially. When tall building is 250 m high and the short building is 150 m high, probabilities of lightning strikes on short building with distance from 50 m to 600 m with interval of 50 m are 8.3%, 15.0%, 26.5%, 36.7%, 39.5%, 47.5%, 58.9%, 57.0%, 56.0%, 57.2%, 61.0%, and 62.5%. When there is a cut-off point where the increasing trend of the probability of lightning strikes on short buildings appears to slow down significantly, the probability of lightning strikes on short building differs from its probability of lightning strikes in isolation by only 3.6%. Comparing the lightning strike results for different building distance and isolated building, the difference in lightning strike results caused by the presence of tall building decreases from 44.5% to 22.7% when the horizontal distance between tall and short buildings is increased from 400 m to 600 m. Given the height of tall building, the probability of lightning strikes on short building with different heights follows a similar trend from a large increase to a flat increase with an inflection point. Corresponding to short building height from 50 m to 200 m, the horizontal distances reaching cut-off point are 300, 450, 550 m and 600 m, respectively. When two buildings are far separated, the effect of tall building on the probability of lightning strikes on short building is weaker, and it can be assumed that there is a state when tall building have no effect on the lightning attachment process.

The data supports the manuscript entitled "A self-sustained charge neutrality lightning model containing the channel decay and reactivation process”. Microsoft Notepad can open the *.txt files, they contain the channel information of two intracloud flashes (IC1 and IC2) and the channel elctrical parameters at the first fork of positive or negative leader channels. A normal video player software can open Movies S1.avi, and it shows the entire development process of IC1 discharge. The data can be used freely for scientific purposes with the appropriate citation.

A self-sustained charge neutrality parameterization scheme of intracloud (IC) lightning is presented in this paper. The scheme contains the following features: simultaneous development of multiple branches, polarity asymmetry of positive and negative leaders, nonlinear electrical parameters, complete charge neutrality, and channel decay and reactivation. Nonlinear electrical parameters and charge neutrality are the key factors that determinate channel decay and reactivation. To demonstrate the simulation capacity of this scheme, two simulated intracloud flashes by this scheme under the tripole charge structure are chosen for analysis. These two IC flashes show clearly the above features, where reactivation processes that initiated from different branches and the real-time changes in nonlinear electrical parameters are mainly analyzed. The simulation results are in line with the current knowledge on lightning, which also suggests that the new scheme may become a useful tool to deeply explore the discharge phenomena involving channel decay and reactivation.

Abstract. The effect of aerosols on lightning has been involved in many studies, but its mechanisms are complex and far from understood. The relationship between cloud-to-ground (CG) lightning and aerosols on an hourly time scale in the Sichuan Basin during 2010–2018 was investigated. The effects of aerosols, dynamics-thermodynamics factors (convective available potential energy: CAPE and vertical wind shear: SHEAR) and cloud-related factors (total column cloud liquid water: TCLW and total column cloud ice water: TCIW) on the CG lightning flashes on day and night were analysed. The diurnal variation of CG lightning flashes has two peaks under clean conditions, while only one peak was found in the diurnal variation of ground flash under polluted conditions. In the early morning and night, more CG lightning flashes were found under polluted conditions, but in other periods, the difference in the CG lightning flashes between polluted and clean conditions is insignificant. Similar results were also found in the percentage of positive CG lightning flashes. At night, aerosols are positively correlated with the CG lightning flashes, and the response of CG lightning flashes to CAPE, SHEAR and TCLW is more evident under high aerosol loading. In the afternoon, aerosols have no significant effects on CG lightning and its response to dynamics-thermodynamics and cloud-related factors. This difference seems to be caused by the different impacts of aerosol radiative and microphysical effects in these two periods. In the afternoon, aerosols may directly (indirectly) reduce the solar radiation reaching the ground and suppress convection through aerosol radiative effects (aerosol microphysical effects). Aerosols may also stimulate convection through microphysical effects. In this period, the two opposite effects of aerosols on convection offset each other. At night, without solar radiation, the aerosol microphysical effects may play a dominant role in the entire AOD range to promote convection.

In this study, a stochastic lightning parameterization scheme is coupled with a dipole charge structure, and the parameters and positions of the main negative charge region are fixed. Positive intracloud（+IC） flashes initiating at different altitudes are simulated by adjusting the parameters（charge concentration and horizontal range） of the upper positive charge region, and then the relationships between the characteristics of the +IC flashes and thunderstorm charge distributions are discussed. Simulation results indicate that in dipole charge structures, the elevation of the upper positive charge region can generate high-altitude +IC flashes, which is consistent with observations. Unlike normal IC flashes that are dominated by upward negative leaders and horizontal or slightly downward positive leaders, IC flashes initiated at high altitudes are characterized by long-distance downward positive leaders and horizontal or slightly upward negative leaders. The initiation altitudes of +IC flashes increase with the elevation of the upper positive charge region. When the upper positive charge region is lifted to a certain altitude（in this paper, the upper positive charge region’s lower boundary altitude is 12 km）, IC flashes are usually initiated from the main positive charge region, and the concentration and horizontal radius of the upper positive charge region have no major effect on the initiation altitude of IC flashes. In addition, the length of positive or negative leader channels has a substantial positive correlation with concentration and horizontal radius of the charge region and the distance between the initiation point and the negative or positive charge region.

The effects of aerosols under special terrain on lightning activities in the Sichuan Basin (SB) are studied using the cloud-to-ground (CG) lightning data and aerosol optical depth (AOD) data from 2010 to 2018. Interesting results show that the topographic drop plays an important role in the process of aerosol affecting lightning. The great topographic drop in the western SB is conducive to the production of CG lightning. Both the CG lightning production and AOD in the northwest and southwest of the basin decrease in fluctuation during the study period. It can be inferred that the reduction of aerosol results in the decrease of lightning activity. Due to the topographic drop in the northwest of the basin being greater than that in the southwest, the correlation of 0.64 between AOD and CG lightning in the northwest of the basin is larger than that of 0.31 in the southwest. Since the lightning activity in SB generally occurs at night, the aerosol-radiation interaction (ARI) has an insignificant influence on the occurrence of convection. Under this condition, it can be inferred that the aerosol-cloud interactions (ACI) are dominant over SB region. These could better support the reduction of lightning generation.