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ALMA MEMO #486

Characteristics Of Lightning Discharges Over AOS


T. Watanabe (Gifu University), N. Takagi (Gifu University),
D. Wang (Gifu University), L. Liu (Gifu University),
M. Kamata (Gifu University), S. Sakamoto (NAOJ)

2004-02-04



Lightning discharges over the Array Operations Site (AOS) were measured with electromagnetic field antennas. A total of 107 lightning discharges recorded in summers of 2002-2003 were statistically analyzed. Although thunderstorms over the AOS are rare, once occurred, strong lightning activity with a lightning frequency of 1.6 flashes per minute and the cloud-to-ground discharge percentage of about 66%, both comparable to summer lightning at lower altitudes was observed. Among cloud-to-ground discharges, about 7% were positive cloud-to-ground discharges that often neutralize large amount of charges. The number of strokes per flash of the cloud-to-ground discharges was very large, with a maximum value of 24 and a median value of 8. The median value of the inter-stroke time interval was very short (25 ms), suggesting shorter distance to the thunderstorm charges. The continuous current component that neutralizes large amount of charges were observed in 39% of the cloud-to-ground discharges, and the median value of the continuous current duration was long (140 ms) and was comparable to that of typical summer lightning at lower altitudes.


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Last modified: 2004-02-04

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