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双层均匀口袋电荷模型下闪电起放电特征的数值模拟研究

Numerical Simulation of the Initiation and Discharge Characteristics of Lightning with the Double-Layer Uniform Pocket Charge Model

  • 摘要: 大量基于观测的研究认为闪电通道的延展尺度与电荷的分布形态息息相关,强对流区频繁始发的小尺度闪电对应雷暴云内的背景电荷很有可能为“口袋电荷”的分布模式。为验证口袋电荷背景下能形成此类云闪并给出该电荷背景下闪电起、放电的一般规律,本研究将闪电放电参数化方案植入到双层均匀口袋电荷模型中开展了大量随机模拟试验。模拟过程中固定了电荷区的总尺度,通过改变电荷对数进行探讨,着重讨论各电荷背景下闪电起始和放电行为的异同。模拟结果表明:(1)随着电荷对数的增加,闪电启动需要的电荷浓度和电荷总量均增加。(2)小电荷区的水平垂直尺度比是影响闪电起始行为的关键因子,除此之外各电荷背景下闪电起始位置和启动概率在水平、垂直方向上的差异还与多对电荷的空间配置关系和逃逸击穿阈值有关。(3)闪电的水平、垂直范围和面积均与小电荷区的尺度息息相关,小电荷区的几何特征限制了闪电的空间特征。(4)电荷区的分布也显著影响着闪电的发展形态,各电荷背景下闪电初始先导角度的分布范围和集中区域有所差异。相较于电荷区倾向于为扁平椭圆形的情况,当电荷区垂直与水平尺度相等时,初始先导角度变化范围明显增大,水平发展的个例明显增多。

     

    Abstract: Numerous observation-based studies have proposed that the extension scale of lightning channels is closely related to charge distribution patterns. They have also proposed that in areas with strong convection, small and frequent lightning is likely to form with the pattern of charge pockets. Herein, the lightning discharge parameterization scheme was coupled with the double-layer uniform pocket charge model, and a large number of random simulation tests were conducted to verify that such cloud flashes can be formed against the background of pocket charge and provide the general law of lightning initiation and discharge with this charge distribution pattern. The total dimension of the charge region was fixed, whereas the pairs of the charge region in the simulation were varied to discuss the similarities and differences of lightning initiation and discharge behavior against each charge background. Simulation results indicate that (1) with the increase in charge pairs, the charge concentration and total charge quantity for lightning startup increase. (2) The axial ratio of each small charge region is the key factor affecting lightning initiation behavior. In addition, the spatial configuration relationship of multiple pairs of charges and the runaway breakdown threshold cause the lightning starting position and probability in the horizontal and vertical directions to differ in each case. (3) The spatial characteristics of lightning are limited by the geometric characteristics of the small charge region. (4) The distribution of the charge region considerably affects the development shape of lightning. Against each charge background, the distribution range and concentration area of initial leader angles differ. The variation range of the initial leader angle and number of horizontal development cases are considerably higher in the case wherein the vertical and horizontal radii of the small charge region are equal to those in the case of the previous charge structure (flat ellipse).

     

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