人工触发闪电通道的发光特征

THE CHARACTERISTICS OF THE CHANNEL LUMINOSITY OF TRIGGERED LIGHTNING FLASHES

利用成像率为１０００幅／秒的高速数字化摄像系统在３８０ｍ的极近距离对人工触发闪电通道的发光特征进行了观测和研究。人工引发闪电除了采用传统的火箭拖带接地导线的触发方式外，还发展了导线下端不接地的空中触发闪电的新技术。结果表明，闪电通道的发光截面基本上呈对称型。各次闪电的发光持续时间和光脉冲的个数可以有很大的差别，但它们都可分成四个共有的发光阶段，并与特定的闪电放电物理过程相联系。闪电的光脉冲与闪电电流脉冲和地面电场变化有很好的对应关系。其中，起始光脉冲由导线汽化和上行先导传播入云所引起；Ｍ分量脉冲出现前闪道仍在可观地发光，而回击光脉冲出现前闪道的发光已经变得非常微弱或已测不到发光现象。空中触发闪电最下部的通道由金属导线汽化通道和空气离化通道两部分组成。它们的发光行为有很大的不同，尤其在平稳发光阶段，前者的发光较强且延续更长的时间。对各种发光成分的特点及其所联系的物理过程也进行了讨论。

The luminous characteristics of the channel of artificially triggered lightning flashes were studied by use of digital photographic data obtained with a high-speed CCD camera system ( frame rate 1 000F/s) at very close range to the lightning. The techniques for triggering lightning were conventional one with a rocket trailing a grounded wire as well as a newly-developed one called altitude-triggering with the lower end of the wire not connected to the ground. The results showed that the transversal distribution of channel luminosity was essentially symmetric. The duration of the channel luminosity and the number of light pulses for individual flash could be different noticeably, however, they had four common luminous phases, which associated with specific discharge processes. The light pulses during a flash were found to well correspond with that of electric field change and lightning current. The initial light pulse was produced by the upward leader propagating into clouds and the vaporization of the wire as a result of leader development; channel had being appreciably luminant when M component occurred; whereas the channel luminosity had become very weak or even ceased when light pulse of return stroke appeared. The lowest part of the lightning channel of an altitude triggered flash consisted of metal-vaporized and air-ionized ones, whose luminous behaviors were quite different: the channel luminosity of the latter was more intensive and lasted for a longer time, especially during the steady luminous period.