Characteristic of Lightning Channel in the Thundercloud from Thunder

点击翻译按钮获取中文摘要

We measured 23 thunder records at Numazu near Mt. Fuji on May in 1992, and at Tubata and Shishiku Heights near Kanazawa in winter since 1990. (1) Thunder signatures are classified into three types. The first type is that the largest sound arrives within 0.5 sec at the outset and after that becomes gradually weaker. The second type is that weak sound comes first and becomes stronger step by step and after that gradually weakens. The third type is that the first or the second type repeats. (2) The mean duration of thunder is 20 sec in winter thunder. The thunder of the third type is observed in winter lightning and has almost long duration more than 30 sec. (3) The dominant frequency of power spectrum is 140 Hz on the average, the nearby thunder less than 5km to main channel is 150Hz, on the other hand the thunder of long distance more than 5km is 67Hz.It is shown that the channels of long duration thunder are reconstructed by determining the time window length from zero-crossing number, and the channels of a multistroke lightning are reconstructed from the dominant thunder signals.The spatial resolution of sound source location is made clear from the relation sampling period of thunder data and microphone configuration. When four microphones are located at the origin and on right angled axes in equal separation of D meaters, the resolution is less than 2ROO<3>DELTAS/D for any directional sounds, where DELTAS is sampling error.The lightning channels are reconstructed from the winter thunder and the following results are derived : (1) Lightning of simultanous strokes to different points presents occasionally the third type of thunder. (2) The center of lightning channels is in the range 1.5km and 2km altitude and the horizontal channel is longer than 15km in horizontal extent.