Numerical Simulation Of The Effect Of Horizontal Distribution Of Space Charge In Thunderstorms On The Lightning Behavior

The charge structure of thunderstorms and its internal charge distribution is an important subject in the field of atmospheric electricity research,because it has a direct impact on the characteristics of lightning discharge.Many studies have deeply investigated the important effect of different charge structures in thunderstorm on lightning discharge in many aspects,such as lightning types,polarity,scales,etc.,but lack quantitative investigation of the effects of the horizontal distribution on the charge structure.For purpose of quantitatively investigating the effect of horizontal distribution forms of space charge in thunderstorms on lightning discharge,based on the existing stochastic lightning parameterization scheme,a thundercloud model was set up in this study.The parameters that control the horizontal distribution of charge(?)was introduced then performed 2-dimensional fine-resolution(12.5m)lighting discharge simulations.In order to eliminate the influence of the vertical charge structure change and the randomness of lightning discharge in thunderstorm,this paper mainly set up three schemes for sensitivity tests,the main research results of each part are as follows:(1)In a typical tripolar thunderstorm cloud(including shielding layer)charge structure,the total amount of charge in the upper positive and main negative charge regions is controlled to be equal.The results shows,when the forms of charge changes from dense unevenness into single uniform,lightning type changes from positive cloud-to-ground(+CG)flashes to positive intra-cloud(+IC)flashes,then into negative cloud-to-ground(-CG)flashes,and finally into positive intra-cloud(+IC)flashes in limited cases.When the distribution of charge levels in the main negative charge region tends to be uniform,the type of lightning changes from-CG flashes to +IC flashes,then to +CG flashes and lastly to +IC flashes.The horizontal distribution of space charge has a significant effect on propagation of lightning leaders,if it is dense uneven,the leaders propagates in the center of the charge density,otherwise,the leaders can extends more than 10 to 20 km in the horizontal direction.(2)The horizontal distribution forms of charge in lower positive region also play a key role on lightning discharge.The results shows,as the horizontal distribution of charge in the lower positive region tends to be uniform,lightning type changes from +CG flashes to inverted intra-cloud(-IC)flashes,finally into-CG flashes.The distance between-CG flashes struke point and the center of the thunderstorm increases first and then decreases(the fitting curve is a parabola)as the charge distribution parameter ? increases.(3)As the horizontal distribution of charge in the charge region tends to be uniform,the potential lines between the two charge regions are concentrated towards the charge density center,and the potential well extendes horizontally,causing the different initial potential values at the lightning trigger points,which result in the generation of different types of lightning and the far-spreading leaders in the horizontal.+CG flashes occured when the initial potential of the lightning trigger point is much greater than OMV(at least 30MV or more),if its initial potential value is close to OMV,IC flashes(+IC or-IC)occured,when the initial potential value is much less than OMV(below-30MV),-CG flashes are more likely to occurs.(4)Set up varieties of different charge vertical structures,the effect of charge distribution on the lightning discharge was discussed.The results show that the vertical charge structure affects the type of lightning through the location of the lightning trigger point,and the horizontal distribution of charge inside the regions changes the distribution of space charge,causing changes in the initial potential,and then produce different types of lightning.