Observation and study on the whole process of cloud-to-ground lightning using narrowband radio interferometer
Observation and study on the whole process of cloud-to-ground lightning using narrowband radio interferometer
复制标题
DOI：
10.1007/s11430-008-0049-9
复制
发表时间：
2008-09
期刊：
影响因子：
--
通讯作者：
Guang-shu Zhang;Yuxiang Zhao;X. Qie;Tong Zhang;Yanhui Wang;Chengpin Chen
中科院分区：
文献类型：
--
作者：
Guang-shu Zhang;Yuxiang Zhao;X. Qie;Tong Zhang;Yanhui Wang;Chengpin Chen
一个窄带无线电干涉仪已经开发出来，并用于定位整个源的VHF辐射从负的云对地（CG）闪电放电，其中包含19个中风。该系统采用五根天线沿沿着两个正交方向形成由短基线和长基线组成的阵列。采用直接高频放大的鉴相方法，减小了变频带来的系统误差。一个交互式的图形分析程序是用来消除条纹的模糊性，固有的存在于干涉测量，并确定闪电辐射源的方向在两个维度（方位角和仰角）作为时间的函数在微秒级的时间分辨率。利用该系统可以再现闪电在时间和空间上的整个发展过程。本文结合电场变化和VHF辐射的同步观测数据，详细研究了一个负电荷地闪的全过程。结果表明，CG闪光的初始击穿事件是从负电荷区开始的，并呈现出先向下传播，然后向上传播的过程。有非常强烈的和持续的辐射在步进领导人变得更强时，第一个回击开始。相比之下，在飞镖领导人期间有较少的，只有离散的辐射。阶梯先导和飞镖先导可以根据路径电离状态相互转化，初始阶梯先导的前进速度约为105 ms-1，飞镖先导和阶梯先导的前进速度分别约为4.1× 106和6.0× 106 ms-1。M事件产生钩形场变化，并伴随着辐射的活跃爆发。在这些活跃的辐射过程之后，M事件似乎最终接触到导电的主放电通道。M事件的平均进展速度约为7× 107 ms −1，大于飞镖领导者和飞镖步领导者。K项目和尝试领先者基本上与飞镖领先者相同，只是他们不能到达地面并开始回击。
A narrowband radio interferometer has been developed and used to locate the entire sources of VHF radiations from a negative cloud-to-ground (CG) lightning discharge which contains 19 strokes. This system uses five antennas to form an array consisting of short-and long-baselines along two orthogonal directions. The system error which comes from frequency conversion is reduced by phase detection through direct high frequency amplifying. An interactive graphic analysis procedure is used to remove the fringe ambiguities which exist inherently in interferometry and to determine the direction of lightning radiation sources in two dimensions (azimuth and elevation) as a function of time at a time resolution of microsecond orders. With the developed system, the whole progression process in time and space of a lightning flash can be reconstructed. In this paper, combining the synchronous data of electric filed change and VHF radiation, the whole processes of an example negative CG flash have been studied in detail. It is found that the preliminary breakdown event of the CG flash started from negative charge region and exhibited firstly a downward pregression and then an upward propagation. There were very intense and continuous radiations during stepped leaders which became much stronger when the first return stroke began. In contrast, there were less and only discrete radiations during dart leaders. Stepped leader and dart leader may transform to each other depending on the state of the ionization of the path. The progression speed of initial stepped leaders was about 105ms−1, while that was about 4.1×106and 6.0×106ms−1for dart leaders and dart-stepped leaders, respectively. M events produced hook-shaped field changes accompanied by active burst of radiations at their beginnings. Followed these active radiation processes, M events appeared to contact finally into conducting main discharge channels. The mean progression speed of M events was about 7×107ms−1, greater than that of the dart leaders and dart-step leaders. K events and attempted leaders were essentially the same as dart leaders except that they could not reach the ground and initiate return strokes.