# A 3D Numerical Model to Estimate Lightning Types for PyroCb Thundercloud
## 1 Introduction
Therefore, there has been considerable focus recently on the specific significance of the lower positive charge region. To date, there has been no literature work on the distribution of charges or investigations into the electrical circumstances conducive to lightning discharges in pyroCb events. The conditions present in pyroCb storms, characterized by strong wind shear and undiluted updrafts, increase the likelihood of exhibiting tripole charge structure while forming pyroCb thunderclouds [10; 11]. Certain studies consider the tilted tripole charge structure in severe thunderstorms, where the charge centers in the upper cloud region are shifted towards the direction of the strong wind shear [23; 24]. This displacement can separate the positive  
Figure 1: (a) Active fire and (b) lightning strike observations on Black Saturday, 7 February 2009 [11]. and negative charge regions, allowing both +CG/\(-\)CG flashes to occur from the displaced positive charge region. In recent years, a method widely used to develop and understand thundercloud charge structures is the physical thundercloud model which incorporates several complex factors, including induced electric charge, the state of lightning leaders, and the formation of corona regions [25; 26; 27]. For analyzing the actual thunderstorm process at the micro-physical level, this method highly relies on observation data, which makes it computationally expensive over large-scale domains. Nowadays, the numerical thundercloud model coupled with the empirical governing equations become widely popular in studying the configuration and dynamics of thunderclouds [18; 23; 24; 28; 29]. This stochastic model based on electrostatic concepts presents the cloud model in an axisymmetric manner, employing the non-inductive charging approach to describe the electrification of the thundercloud. Although this modeling technique is complex and requires significant time, it is remarkably efficient in capturing the dynamic evolution of a thundercloud that could be useful to identify the precise locations on Earth's surface or any object in danger due to thunder or lightning. Previous studies [30; 31; 32; 33] have shown that aerosols affect cumulus clouds, implying that aerosols generated by fires might influence the formation of pyroCbs. For cumulus clouds, an increase in aerosol concentration leads to the formation of a large number of smaller cloud droplets. This process lowers the efficiency of droplet collisions, which delays and inhibits the formation of raindrops. Studies in [34; 35; 36; 37; 38; 39] have identified a positive correlation between lightning activity and aerosol concentrations. Additionally, those works demonstrate that high aerosol concentrations can significantly enhance the electrification process, according to the bulk microphysical model, or even weaken the electrification on further increase. However, the scientific community still lacks a thorough understanding of fire-induced aerosols' role in forming pyroCb thunderclouds and their electrification process. There is limited research on how variations in aerosol loading affect pyroCb development, with only a handful of studies conducted to date [40; 41; 42]. In this paper, a 3D stochastic thundercloud model is demonstrated to simulate the conceptual tripole cloud structure, which is proposed as a representation of a pyroCb thundercloud. More attention is placed on the lower positive charge layer to comprehensively analyze different electric states that benefit CG flash generations. In addition, the behavior of the pyroCb thundercloud under strong wind shear is investigated. The suggested model demonstrates how alteration in the size and intensity of the charge layers can impact both thundercloud potential and field distributions, along with surface charge density. Lastly, the model is utilized to investigate how varying aerosol concentrations impact the electrical parameters which may help to obtain a parametric knowledge of how the smoke-induced aerosols influence the lightning process in pyroCb.