Numerical Simulation of the Effects of Thunderstorm Charge Distributions on the Discharge Characteristics of Positive Intracloud Lightning Flashes

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.