Characteristics of the Electric Field Waveforms Associated with Lightning Return Strokes

초록

This paper describes the fine structure of electric waveforms produced by lightning return strokes. The electric measuring system consists of heisphere antenna 30cm in diamete, integrator and data acquistion device. Its frequency bandwidth is from 200Hz to 1.56MHz and the sensitivty is 0.96mV/V/m. The electric field signals are digitized every 200ns with the resolution of 12bit and the length of 5kilowords, and those are registered by a personal computer. Also the data is analyzed by means of the fast Fourier transform(FFT) method. The electric field waveforms associated with lightning return strokes are observed during the summer of 1995 at the campus of Inha University, in Inchon, Korea. The electric field radiated by the first return strokes beings with slow initial part or wave front, which starts just after or during the last stepped leader. The electric field waveform rises abruptly to a peak and most electric fields have one or more second peak immediate following the first peak. The electric field waveform due to the first return stroke has several subsidiary peak with amplitudes, which decrease with time. The electrical field waveforms radiated by intracloud discharges tend to be bipolar with two or more narrow and several pulses superimposed on the initial rising part.