HR: 09:08h
AN: AE41A-06    [Abstracts]
TI: Upward Lightning Flashes Observed at the 200-m Fukui Chimney in Winter
AU: * Wada, A
EM: jun@criepi.denken.or.jp
AF: Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka-shi, Kanagawa-ken, 240-0196 Japan
AU: Miki, M
EM: megu@criepi.denken.or.jp
AF: Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka-shi, Kanagawa-ken, 240-0196 Japan
AU: Asakawa, A
EM: asa@criepi.denken.or.jp
AF: Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka-shi, Kanagawa-ken, 240-0196 Japan
AB: The study of upward lightning flashes is very important for the lightning protection methods of tall structures. For over twenty years we have been observing the lightning discharge at the 200-m Fukui chimney in winter in Japan for clarifying winter lightning characteristics. About thirty to forty events of the lightning flashes are observed in a winter season. About ninety percent of all the recorded events were the upward lightning flashes initiated by an upward moving positively charged leader. About ten percent was the lightning initiated by an upward moving negatively charged leader. Some of the lightning produced the subsequent discharge composed of downward leader and upward return stroke sequences following the upward leader development. Two-dimensional average speed of upward moving positive leader was 3.6x105 m/sec with a range from 0.6x105 to 14x105 m/sec. Most positive leader progressed upward without any appreciable stepped motion. In the lightning initiated by the upward positive leader, the lightning discharge processes are categorized in four types. Type a: upward positive leader only. Type b: upward positive leader and downward return stroke sequences. Type c: downward negative leader and upward return stroke sequences following the upward positive leader development. Type d: downward positive leader and upward return stroke sequences following the upward positive leader development. Most upward-initiated lightning was observed without return strokes, as type a. Type b is a rare case. After the upward positive leader developed at a speed of 2.3x106 m/sec, downward return stroke was observed at average speed of 1.6x108 m/sec. The downward return-stroke decreased the speed from 2.5x108 m/sec to 2.5x107 m/sec as it developed towards the ground. Type c is similar to the lightning from the Empire State Building and the _gclassical triggered lightning_h of the rocket-triggered lightning. Type d is a new type of lightning discharge process from the tall structure in winter. The lightning flash initiated by the upward negative leader is rare case and it is very hard to observe it. One example was observed with a good condition. The average speed of the upward leader was 6x106 m/sec and the mean value of each step speeds was 3x107 m/sec. The upward leader moved with stepped motion like a downward stepped-leader of natural lightning in summer. Interestingly, the step length, the speed, and the peak current increased as the upward leader development and the measured upward leader current is big compared to the estimated downward leader current.
DE: 3324 Lightning
DE: 3304 Atmospheric electricity
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting