# A 3D Numerical Model to Estimate Lightning Types for PyroCb Thundercloud
## 3 Simulation Results and Discussion  
### Tripole Structure with Large Lower Positive Charge  
To investigate whether a large LP charge region affects the electrical conditions to generate CG lightning, simulations are carried out on two different configurations of pyroCb thundercloud with a tripole structure. Figure 3a,b illustrate the cross-sectional view of the simulated tripole charge configurations. These charge configurations are built at the midpoint of the \(y\)-axis within the computational space, specifically along the \(xz\) plane. The electric potential generated by the tripole structure is analyzed and illustrated in Figure 4(a1,a2) and Figure 4(b1,b2), respectively. When the LP charge region of the pyroCb thundercloud is enhanced in the second configuration (Figure 3b), the overall potential of the pyroCb thundercloud shows a positive increment compared to its first configuration depicted in Figure 4(a2). With a relatively large LP charge, the magnitude of the electric field within the thundercloud decreases as evident in Figure 4(b2) in comparison to Figure 4(b1). This observation aligns with the characteristics dictated by the law of the electrostatic field. Figure 4: Plots of the distributions of electric potential (**a1,a2**) and the changes in the electric field (**b1,b2**) for configurations 1 and 2 of the tripole structure-based pyroCb thundercloud, respectively. Figure 3: The vertical profile of the pyroCb thundercloud model (in xz plane) exhibits a tripole charge structure under two different conditions: (**a**) without LP charge enhancement (configuration 1) and (**b**) with increased LP charge region (configuration 2). Illustrating two distinct configurations of the pyroCb thundercloud, Figure 5(a1,a2) and Figure 5(b1,b2) display the projected electric potential values at the maximum field and longitudinal electric field, respectively. These are measured along the \(z\)-axis at the core (at \(x=15\) km and \(y=15\) km) of the simulation domain. In Figure 5(a1,a2), the symbol \"x\" denotes the particular node point where the maximum electric field with discharge initiation occurs. The mathematical expression in (6) [45] represents the relationship between altitude \(z\) and the initiation threshold value \(E_{th}(z)\), marked as red dotted lines in Figure 5(b1,b2). As observed in Figure 5(a1,a2), the maximum potential shows gradual incremental trends while the minimum potential decreases when the LP charge region is enhanced. At the same time, the lightning flash initiation point of the pyroCb thundercloud has shifted from \(-51.73\) MV (in the first configuration) to a positive value of \(203.397\) MV in the second configuration. This analysis agrees with the findings reported in [46], which indicate that the CG lightning initiation (regardless of their polarity) occurs only when the absolute potential value at the initiation point is significantly higher than \(0\) MV. In contrast to the first configuration, the longitudinal electric field (\(E_{z}\)) at the thundercloud bottom exhibits a negative shift with the increase in the LP charge layer (Figure 5(b2)). \[E_{th}(z)=\pm 201.7 exp\bigg{(}-\frac{z}{8.4}\bigg{)} \tag{6}\]  
The results of simulated surface charge density \(\sigma\) on Earth's surface are graphically presented in Figure 6a and 6b, respectively, for two different configurations of pyroCb thunderclouds. This analysis helps in understanding the probable lightning types associated with two distinct tripole charge setups and is summarized in Table 2. As observed in the first configuration (Figure 6a), surface charge density \(\sigma\) becomes positive within the ranges  
Figure 5: Graphs depicting the electric potential \(V\) (MV) are shown at the point of maximum field where the initiation of flash is marked with an “x” (**a1,a2**). The longitudinal electric field \(E_{z}\) (\(\mathrm{K}V/\mathrm{m}\)) for two different thundercloud configurations is also illustrated in (**b1,b2**).