Electric field pulses in K and M changes of lightning ground flashes
Electric field pulses in K and M changes of lightning ground flashes
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DOI：
10.1029/92jd00797
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发表时间：
1992-06
影响因子：
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通讯作者：
V. Rakov;R. Thottappillil;M. Uman
中科院分区：
文献类型：
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作者：
V. Rakov;R. Thottappillil;M. Uman
从佛罗里达州坦帕附近的27次地面闪光和美国宇航局肯尼迪航天中心（KSC）的19次地面闪光的电场记录中，研究了微秒级电场脉冲的发生和波形，这些脉冲与毫秒级阶梯K变化和毫秒级钩形M变化有关，以检验和反驳以下两个假设：(1) K变化包含微秒级脉冲分量，可以用Arnold和Pierce（1964）提出的特征脉冲波形来描述；(2)Kitagawa等人（1962）认为K和M过程本质上没有区别。在坦帕的135 K变化中，微秒尺度的电场变化至少超过系统噪声水平的50%，在KSC的128 K变化中，微秒尺度的电场变化占25%，而在坦帕的88 M变化中，这种电场变化占44%，在KSC的30 M变化中，这种电场变化占77%。在大多数具有微秒级脉冲活动的K变化中，该活动不会发生在K步的开始，而在大多数情况下，与M变化相关的脉冲发生在M钩子的初始部分。这些结果可以解释为暗示K变化和M变化与不同的物理过程有关，反驳了上述假设(2)。在K和M变化过程中，微秒尺度的脉冲活动变化很大，有时波形不规则。并非所有脉冲的极性都与K阶跃或M阶跃的初始部分相同。在发生频率、脉冲在较慢场内的位置变化以及脉冲形状方面，微秒尺度的变化与地面闪光中K的总体变化之间的关系与Bils等人（1988）报道的云闪光中K的变化相似。观测到的与K变化相关的微秒尺度电场变化与Arnold和Pierce（1964）等研究者对K变化的特征电场脉冲波形不一致，反驳了上述假设(1)。没有观察到K变化的大小与相应的微秒尺度场变化的存在与否之间的关系。相对于持续时间较长的持续电流场变化，持续时间较短（小于20ms左右）的M变化更容易产生脉冲。
From electric field records of 27 ground flashes near Tampa, Florida, and 19 ground flashes at the NASA Kennedy Space Center (KSC) the occurrence and waveshape of microsecond-scale electric field pulses associated with both millisecond-scale steplike K changes and millisecond-scale hook-shaped M changes are examined to test and disprove the following two hypotheses: (1) that K changes contain a microsecond-scale pulse component which can be described by the characteristic pulse waveform proposed by Arnold and Pierce (1964) and (2) that there is essentially no difference between K and M processes, as argued by Kitagawa et al. (1962). Microsecond-scale electric field variations exceeding by at least 50% the system noise level were observed in 23% of 135 K changes from Tampa and in 25% of 128 K changes from KSC, while such field variations were found in 44% of 88 M changes from Tampa and in 77% of 30 M changes from KSC. In the majority of the K changes having microsecond-scale pulse activity, that activity did not occur at the beginning of the K step, while in most cases the pulses associated with M changes occurred at the initial portion of the M hook. These results can be interpreted to imply that K changes and M changes are associated with dissimilar physical processes, in refutation of hypothesis (2) above. The microsecond-scale pulse activity during K changes and M changes was highly variable and sometimes irregular in waveshape. Not all the pulses had the same polarity as the K step or the initial portion of the M hook on which they were superimposed. The relation of the microsecond-scale variations to the overall K changes in ground flashes as regards the frequency of occurrence, the position of pulses within the slower field change, and the shape of the pulses is similar to that reported by Bils et al. (1988) for K changes in cloud flashes. The observed microsecond-scale field variations associated with K changes are not consistent with the characteristic electric field pulse waveform attributed by Arnold and Pierce (1964) and some other investigators to K changes, in refutation of hypothesis (1) above. No relation was observed between the magnitude of a K change and the presence or absence of corresponding microsecond-scale field variations. M changes during continuing-current field changes of relatively short duration (less than 20 ms or so) are more likely to have pulses than M changes during continuing-current field changes of longer duration.