The characteristics of charge in lightning channel are the focus of lightning physics research, yet it is difficult to directly obtain detailed evolution characteristics of charge in the channel using existing observation methods. In order to further study the variation characteristics of charge in lightning channel and complement the lightning detection technology, it is necessary to carry out model work. Using the Self-Sustained Charge Neutrality Intracloud Lightning Parameterization model, multiple intracloud flashes are simulated under the three-pole charge background and a typical case is selected. The variation characteristics of channel charge and their influencing factors are analyzed. The results are as follows: A certain amount of positive or negative polarity initial charge will deposit in the channels when these leader channels first form. When the subsequent branch extends, the previous channel will deposit heteropolar charges from the subsequent branches, and the charge of the initial polarity in the channel will be continuously neutralized, while the polarity of some channels may change. The charge in the channel will not change if the channel has decayed or its subsequent branches stop extending. When the re-breakdown process occurs, the heteropolar charge in the cut-off channel will be significantly reduced, and the heteropolar charge in the reactivated channel will be significantly increased. The research shows that the charge variation in the leader channel is related to the state of the channel itself and the extension of the subsequent branches. The amplitude of charge change in the channel is positively correlated with the initial charge and the activity of subsequent branches, and the initial charge is positively correlated with the first breakdown electric field. In addition, under the influence of polarity asymmetry between positive and negative leaders, the initial point of intracloud lightning tends to deposit more positive charges.

To explore the initiation and propagation of upward leader (UL) in the cloud-to-ground lightning attachment process, on the basis of the existing multiple upward leaders (MULs) three-dimensional model and considering optical observations and environmental electric field, the background electric field module is implanted and the UL and downward leader (DL) modules are improved. Sensitivity experiments are then carried out using the improved model. The results are as follows: (1) The new model can simulate a variety of DL, and the number of its branches is greatly reduced. Also, the model can well reproduce various cloud-to-ground lightning attachment processes. (2) Statistical analysis of simulation results shows the UL length, striking distance and the frequency of MULs originating from a structure are positively correlated with the structure height. (3) In addition, as the height of the building increases, the initial time difference between the MULs that start successively in the same lightning attachment process shows an overall upward trend. Preliminary research results indicate that the structure height has a significant impact on the initiation of MULs. And due to the influence of the structure height and the positive and negative leaders, MULs triggered by a low structure start almost at the same time, while on the tall structure, the first UL can propagate a certain distance before initiating subsequent UL.

To improve the simulation capability of the numerical model for the fine lightning discharge process, complement the developing lightning detection technology, and explore the relationship between re-breakdown process and thunderstorm electrical parameters, a complete lightning parameterization scheme with a self-sustained charge neutrality is established. This scheme can simulate the cut-off and re-breakdown process of leader. Considering the polarity asymmetry, different extension velocities and initiation and propagation thresholds are set for positive and negative leaders respectively. New non-linear electrical parameters such as channel conductivity, average current, and charge are added to the scheme, and real-time updates of these parameters drive the development of lightning channel while different channel state change thresholds are also set. The real-time state changing leader channels, including decay, cut-off, and reactivation process, are simulated by all the above settings. Based on real-time changes in channel average current, longitudinal E-field and conductivity, charge is redistributed in the space to ensure the self-sustained charge neutrality of channels, which is an important basis for simulating the re-breakdown process. The new scheme is employed in the classical thunderstorm cloud model with tripolar charge structure, and the simulated IC flashes are in good agreement with existing observation facts in terms of channel structure, extinguishment and reactivation of the leader, and the polarity asymmetry of positive and negative leader. The verification against observation facts and some conceptual models indicates that the scheme is reasonable and advanced in simulating the complete lightning discharge process, including extinguishment and re-breakdown process under the premise of self-sustained charge neutrality.