微秒时间尺度脉冲活动是K过程的一个必要特征吗?

Is the Microsecond-Scale Pulse a Necessary Feature of Lightning K Process?

为了澄清微秒时间尺度脉冲活动是否属于K过程的一个必要特征,分析了16次地闪和12次云闪后期对应电场K变化期间的VLF/LF(磁场)脉冲活动和VHF辐射特征。结果显示,微秒时间尺度脉冲活动是K过程的一个必要特征:(1)绝大多数K过程其VLF/LF脉冲活动表现为一个密集的小幅度脉冲簇,脉冲间隔从几微秒到十几微秒不等,其幅度比同期地闪回击幅度弱一个数量级,偶尔上面叠加了与地闪回击幅度可以比拟的大脉冲;(2)另有一部分K过程VLF/LF脉冲活动则类似于地闪或者云闪初始击穿过程的大双极性脉冲列。K过程同时伴随了准连续的Q噪声形态和分立脉冲形态的VHF辐射,这些VHF辐射倾向于与VLF/LF脉冲活动同时在K阶梯电场变化一开始即启动并伴随着K阶梯电场变化,但是二者之间并不存在固定的强度对应关系。K过程放电期间,这些VLF/LF脉冲源的入射方位演变特征表明,它们产生于一个云内不断扩展的源。K过程微秒时间尺度脉冲活动和VHF辐射特征以及它们与K变化之间的时间对应关系支持K过程是云内流光过程的结论。

Simultaneous VLF/LF magnetic fields and VHF emissions associated with K changes from the later portion of 16 cloud-to-ground lightning flashes and 12 intra-cloud lightning flashes were examined to clarify whether the microsecond-scale pulse activity is a necessary feature of K process of lightning discharges.Our results indicate that the microseconds-scale pulse is a necessary feature of K process：（1） the overwhelming majority of K changes have their VLF/LF magnetic fields characterized by a small-amplitude train of dense narrow pulses occurring regularly or irregularly,with sometime one or more large pulses randomly superimposing on it.The width of individual narrow pulse ranges a few microseconds and the average pulse separation is in the order of ten microseconds.（2） A small fraction of K changes were associated with VLF/LF magnetic fields dominated by one or more large pulses which were similar to those occurring during the initial breakdown of cloud-to-ground or/and intra-cloud flashes.K processes were also accompanied by VHF emissions of Q-noise type or separated pulse type.These VHF emissions tend to correlate with VLF/LF magnetic fields in time and occur at the beginning of K changes.The incidence azimuth of VLF/LF magnetic pulses were calculated to change regularly during K changes,possibly implying that the microsecond-scale VLF/LF pulses of K process were produced when the K streamer extended the in-cloud lightning channel.