Preliminary breakdown of intracloud lightning: Initiation altitude, propagation speed, pulse train characteristics, and step length estimation
Preliminary breakdown of intracloud lightning: Initiation altitude, propagation speed, pulse train characteristics, and step length estimation
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DOI：
10.1002/2015jd023546
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发表时间：
2015-09
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影响因子：
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通讯作者：
Ting Wu;S. Yoshida;Y. Akiyama;M. Stock;T. Ushio;Z. Kawasaki
中科院分区：
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作者：
Ting Wu;S. Yoshida;Y. Akiyama;M. Stock;T. Ushio;Z. Kawasaki
利用由11个站点组成的低频闪电定位系统，我们在2013年夏季在日本大坂地区定位了662次云内（IC）闪电的初步击穿（PB）过程。在三维定位结果的基础上，我们研究了PB过程的起始高度和向上传播速度。在大多数IC闪光中，PB的起始高度范围为5 - 10 km，平均为7.8 km。垂直速度范围为0.5 - 17.8 × 105 m/s，平均为4.0 × 105 m/s。垂直速度与起燃高度密切相关，在PB阶段，起燃高度越高，垂直速度越低。分析了PB脉冲序列的脉冲频率、脉冲幅度和脉冲宽度等特性。脉冲频率和垂直速度之间的关系具有最强的相关性，这表明每个PB脉冲对应于PB阶段的初始领导者的一个步骤。脉冲频率、脉冲幅度和脉冲宽度均随起爆高度的增加而减小，随垂直速度的增加而增大。使用一个简单的模型，在PB阶段的初始领导人的步长估计。大多数初始领导者的步长在40到140米之间，平均为113米。估计步长与起始海拔高度有很强的相关性，表明在较高海拔开始的领导者有更长的步骤。根据研究结果，我们推测在一定高度（~12 km）以上，IC闪PB阶段的初始先导可能只具有水平传播。极高高度的PB过程也可能具有非常弱的辐射，因此探测和定位它们将相对困难。
Using a low‐frequency lightning location system comprising 11 sites, we located preliminary breakdown (PB) processes in 662 intracloud (IC) lightning flashes during the summer of 2013 in Osaka area of Japan. On the basis of three‐dimensional location results, we studied initiation altitude and upward propagation speed of PB processes. PB in most IC flashes has an initiation altitude that ranges from 5 to 10 km with an average of 7.8 km. Vertical speed ranges from 0.5 to 17.8 × 105 m/s with an average of 4.0 × 105 m/s. Vertical speed is closely related with initiation altitude, with IC flashes initiated at higher altitude having lower vertical speed during PB stage. Characteristics of PB pulse trains including pulse rate, pulse amplitude, and pulse width are also analyzed. The relationship between pulse rate and vertical speed has the strongest correlation, suggesting that each PB pulse corresponds to one step of the initial leader during the PB stage. Pulse rate, pulse amplitude, and pulse width all show decreasing trends with increasing initiation altitude and increasing trends with increasing vertical speed. Using a simple model, the step length of the initial leader during the PB stage is estimated. Most of initial leaders have step lengths that range from 40 to 140 m with an average of 113 m. Estimated step length has a strong correlation with initiation altitude, indicating that leaders initiated at higher altitude have longer steps. Based on the results of this study, we speculate that above certain altitude (~12 km), initial leaders in PB stages of IC flashes may only have horizontal propagations. PB processes at very high altitude may also have very weak radiation, so detecting and locating them would be relatively difficult.