Observation and study on the whole process of cloud-to-ground lightning using narrowband radio interferometer |
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| Authors: | GuangShu Zhang YuXiang Zhao XiuShu Qie Tong Zhang YanHui Wang and ChengPin Chen |
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| Institution: | (1) Laboratory for Climate Environment and Disasters of Western China, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, 730000, China;(2) Laboratory for Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China;(3) Tianshui Normal College, Tianshui, 741001, China |
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| Abstract: | 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 105 ms−1, while that was about 4.1×106 and 6.0×106 ms−1 for 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 7×107 ms−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.
Supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-YW-206-2), the National
Natural Science Foundation of China (Grant No. 40775004) and the National Science Fund for Distinguished Young Scholars (Grant
No. 40325013) |
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| Keywords: | lightning narrowband interferometer dart leader K events M events the whole process of cloud-to-ground lightning |
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