[asac][almanews] ALMA Memo 486 Released

[Stacy Oliver]

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. 

View a pdf version of ALMA Memo #486.
http://www.alma.nrao.edu/memos/html-memos/alma486/memo486.pdf

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