Observations of preliminary breakdown from negative cloud-to-ground flashes at close range
Preliminary breakdown(PB) from negative cloud-to-ground flashes had been observed at close range. Two orthogonal components of horizontal magnetic field and simultaneous electric field change from 25 PB pulse trains were obtained. The polarity of electric field during the preliminary breakdown is opposite to that of the succeeding return stroke, indicating that these flashes have a distance of several kilometers or less. Magnetic field of PB consists of a series of large pulses, each of which is basically bipolar with one or more small pulses superimposed on the initial rise. The electric field change corresponding to each magnetic pulse is hook-shaped or step-shaped, with a small pulse occurring at the beginning of electric field change in many cases. Coupled with close range electromagnetic field calculations we speculate that a local current propagating along a short channel at a speed comparable to light speed can be responsible for these electric field changes and magnetic fields. Azimuth of PB pulse trains are also calculated using two orthogonal components of horizontal magnetic field. It’s exciting to find that azimuth of PB pulse trains is basically two-layer distributed, that is, some of pulses have a azimuth which is quite different from that of the other pulses. We argue that more than one active source regions were presented during the preliminary breakdown of negative cloud-to-ground flashes.
Helin Zhou Baoyou Zhu Shanchang Tao
School of Earth and Space Sciences, University of Science and Technology of China,Hefei, 230026,China
国际会议
第13届国际大气电学会议(The 13th International Conference on Atmospheric Electricity)
北京
英文
2007-08-13（万方平台首次上网日期，不代表论文的发表时间）