Statistical Analysis of Electric and Magnetic Fields due to Multiple Cloud Lightning Discharges

초록

this paper deals with the statical analysis of electric and magnetic fields associated with multiple cloud lightning discharges. The electric and magnetic field waveforms measured with the hemisphere type electric field sensor and the loop type magnetic field sensor. The frequency response characteristics of the electric and magnetic field measurement systems range from 200Hz to 1.56MHz and 270Hz to 2.3MHz, respectively. And the response sensitivity were 1.04V/m/mV and 7.81nT/mV for each measuring system. The electric and magnetic field waveforms radiated by cloud lightning discharges tend to be bipolar and several superimposed pulses appear at the initial font part of the primary discharge. The occurrence number of the positive and negative stokes obtained from magnetic field waveforms are 3.23, and 3.42, respectively. The ratio of the second subsequent peak amplitude to the first peak was about 70∼80 ％. The time interval between successive strokes is decreased with increasing the stoke number and this result has appeared in both the postive and neagative field waveforms. The mean time interval between superimposed pulses, which appears on the inital front part of the first stoke waveform, is about 4μs and the occurence number is about 2. The percentagedepth of the dip of cloud lightning discharges is about 60∼80 ％. The standard deviations of all field waveform parameters are generally larger for the postive field waveforms than for the negative.