Effects Of Charge Redistribution After Discharges On The Charge Structure Of Thunderstorms And Lightning Characteristics

To investigate the effects of the charge redistribution after discharges on the lightning characteristics ,a three-dimensional (3-D) cumulus model with electrification and lightning process is coupled with two different schemes of charge redistribution .One scheme called ZR scheme for short is that the induced charges are added with the space charges along the lightning channels, and the other one called ZH scheme for short is that the charge density along the lightning channels is reduced by a certain percentage. Sensitivity experiments are performed by using the sounding data in Changchun to analyze the difference of the discharge results under the two different schemes of charge redistribution. Besides,sensitivity experiments are performed to discuss the effects of the induced charges in ZR scheme and the neutralized charges in ZH scheme on the discharge results. What's more, simulations of more cases are performed to verify the simulated results.The main results are as follows:(1) The intra-cloud flash rate in ZR scheme is less than that in ZH scheme.In ZR scheme a lot of charges with opposite polarity are embedded in the charge region after discharges,and more charges are neutralized in ZR scheme than in ZH scheme ,which causes the electric field in ZR scheme to drop more sharply,so there is less intra-cloud flash in ZR scheme.(2)The positive and negative cloud-to-ground flash rate in ZR scheme is more than that in ZH scheme, and the ratio of intra-cloud flash rate to cloud-to-ground flash rate in ZR scheme is less than that in ZH scheme. Compared with ZH scheme,the imbalanced degree between the main positive charge region and the main negative charge region in ZR scheme is more higher, leading to more positive cloud-to-ground flash rate in ZR scheme. Meanwhile, the degree of mixing of the shielding charge region at the cloud top with the main positive charge region is higher and the time of mixing is longer in ZR scheme,so more negative cloud-to-ground flash initiated between the positive charge region and the lower negative charge region is triggered in ZR scheme. Especially in the early stage of the developing thunderstorms,more negative cloud-to-ground flash is triggered because it is easier for the main positive charge region to mix with the top shielding charge region.(3) The lightning channel length in ZR scheme is shorter than that in ZH scheme.Charges with opposite polarity are embedded in the charge region,and it's difficult to form large charge regions with the same polarity. The transmission of the lightning channel is limited to a couple of small charge regions with the opposite polarity in ZR scheme. However,the distribution of the charge regions in ZH scheme is not changed and there are large charge regions with the same polarity,and the range of the transmission of the lightning channel could be larger.(4) Less induced charges in ZR scheme cause less neutralized charges,which leads to more intra-cloud flash.However,the cloud-to-ground flash rate is not increased because the charge distribution is changed and the cloud-to-ground flash is related to the charge distribution.Less neutralized charges in ZH scheme cause more intra-cloud flash and cloud-to-ground flash.The charge distribution is not changed,so the cloud-to-ground flash is also increased.