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Spatiotemporal characteristics of positive cloud-to-ground lightning discharges and bidirectional leader of the lightning
作者姓名:Krehbiel  Paul
摘    要:The negative CG lightning discharges neutralizing negative charges in cloud usually dominate for most of thunderstorms. However, a lot of positive CG light-ning discharges often occur in the disappearing stage of thunderstorms, in the stratiform region of mesoscale convective systems and some supercells producing hail and tornado. Because the positive CG lightning discharges produce larger current of the return stroke and neutralize more charges due to the continuing currents with longer las…

收稿时间:31 January 2005
修稿时间:4 July 2005

Spatiotemporal characteristics of positive cloud-to-ground lightning discharges and bidirectional leader of the lightning
Krehbiel Paul.Spatiotemporal characteristics of positive cloud-to-ground lightning discharges and bidirectional leader of the lightning[J].Science in China(Earth Sciences),2006,49(2):212-224.
Authors:ZHANG Yijun  MENG Qing  Krehbiel Paul  LIU Xinsheng  YAN Muhong  ZHOU Xiuji
Affiliation:1. Chinese Academy of Meteorology Sciences, Beijing 100081, China
2. New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA
3. Cold and Arid Regions Environmental & Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China
Abstract:The three-dimension spatiotemporal development characteristics of positive cloud-to-ground (CG) lightning discharges have been analyzed by using the data measured by the lightning mapping array system with high time and space resolution. The results indicate that a positive CG lightning discharge can be divided into three stages based on the characteristics of its development. The first stage is discharge process in cloud with a long duration preceding the return stroke. This process with an average of 370 ms propagated at velocity of 105 m/s and produced intensive radiation with a magnitude equal to that of the negative leader. During this stage, the lightning channels developed horizontally in the positive charge region with few branches as the negative polarity breakdown. During the stage after the return stroke of the positive CG lightning, the lightning channels propagated at velocity of 2 times faster than that before the return stroke. This stage involved lots of positive fast impulses and corresponded to the continuing current process producing less and dispersed radiation points and more intensive radiation powers. During the final stage of the positive CG lightning, the lightning channels developed at velocity equal to that before the return stroke and the radiation points appeared mainly at the ends of channel. The spatiotemporal development characteristics of the positive CG lightning are very different from that of the negative CG lightning. All of the radiation points of the positive CG lightning appeared in the positive charge region of cloud. Little or no radiation was detected during the positive leader just before the return stroke. The duration of the positive CG lightning was an average of 730 ms. The positive CG lightning discharges with lasting time of 500–600 ms were 43%. 90% of the positive CG lightning discharges involved one return stroke, the most return stroke number being four. The current of the return stroke was an average of 36.5 kA with maximum and minimum values of 70 kA and 11.5 kA respectively. 40% of the return stroke currents were more than 40 kA.
Keywords:positive CG lightning  radiation characteristics  bidirectional leader    
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