Properties of preliminary breakdown processes in Scandinavian lightning
Properties of preliminary breakdown processes in Scandinavian lightning
复制标题
DOI：
10.1016/j.jastp.2008.08.013
复制
发表时间：
2008-12
影响因子：
1.9
通讯作者：
J. Makela;N. Porjo;A. Mäkelä;T. Tuomi;V. Cooray
中科院分区：
文献类型：
--
作者：
J. Makela;N. Porjo;A. Mäkelä;T. Tuomi;V. Cooray
闪电之前通常有初步击穿过程（PBPs），然后才启动梯级引线。这些分解过程还没有被很好地理解。一个早期的模型，即所谓的BIL模型，在后来的研究中受到了质疑。然而，我们发现，至少在高纬度的斯堪的纳维亚闪电中，BIL模式在描述初始过程方面相当成功。我们介绍了芬兰一个夏天的测量结果，在此期间，用标准宽带板天线系统测量了垂直电场。雷电探测网络提供了闪电的位置，用实验窄带探测系统测量了磁场。研究了193次距离为5 ~ 70km的闪光的初步击穿与第一次回击冲程的关系。我们可以在至少90%的闪光中识别出初步故障。RS的峰值电场强度平均是PBP峰值的四倍。然而，在25%的病例中，PBP峰值更为强烈。另一方面，我们证明了这种比较强度的方法在物理上是任意的，因为PBP是连续的，RS是脉冲的。窄带测量允许物理上一致的强度定义为信号中最强烈部分的均方根（RMS）和。在小距离处，PBP和RS的强度几乎相等。距离越远，PBP减弱得越快。这可能是由于不同的传播机制，随着距离的增加，PBP信号从空间波转变为地波传播，而RS在所有距离上都主要是地波。研究结果在窄带雷电探测中具有实际应用价值。BIL模型在窄带信号中提出了一个特征信号，可以用来识别闪电的开始。RS-PBP比作为距离函数的变化在统计上是显著的，但太弱而无法显著改进测距方法。
Lightning flashes are usually preceded by preliminary breakdown processes (PBPs) before a stepped leader is initiated. These breakdown processes are not well understood. An early model, the so-called BIL model, has been called into question in later studies. However, we have found that the BIL model is quite successful in describing initial processes at least in high-latitude Scandinavian lightning. We present results from one summer of measurements in Finland, during which the vertical electric field was measured with a standard broadband plate antenna system. Lightning flash locations were provided by a lightning detection network and magnetic fields were measured with an experimental narrowband detection system. The relationship between the preliminary breakdown and the first return stroke (RS) is studied for 193 flashes at distances of 5–70km. We can identify a preliminary breakdown in at least 90% of the flashes. The peak electric field of the RS is on average four times as intensive as the highest peak of the PBP. However, in 25% of the cases the PBP peak is more intensive. On the other hand, we show that this method of comparing intensities is physically arbitrary, since the PBP is continuous and the RS is impulsive. The narrowband measurement allows a physically consistent definition for intensities as the root-mean-square (RMS) sum of the most intense parts of signals. The PBP and RS are shown to have almost equal intensities at small distances. At larger distances, the PBP weakens more rapidly. This is suggested to be due to different propagation regimes, with the PBP signal changing from space-wave to ground-wave propagation with increasing distance, while the RS is predominantly ground wave at all distances. The result may have practical applications in narrowband detection of lightning. The BIL model suggests a characteristic signal in the narrowband signal, which could be used to identify the start of a lightning flash. The change in the RS–PBP ratio as a function of distance is statistically significant, but is too weak to significantly improve ranging methods.