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| Titel |
Observations of multi-microsecond VHF pulsetrains in energetic intracloud lightning discharges |
| VerfasserIn |
A. R. Jacobson, R. H. Holzworth, X.-M. Shao |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 29, no. 9 ; Nr. 29, no. 9 (2011-09-16), S.1587-1604 |
| Datensatznummer |
250017089
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| Publikation (Nr.) |
 copernicus.org/angeo-29-1587-2011.pdf |
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| Zusammenfassung |
Certain intracloud lightning discharges emit energetic, multi-microsecond
pulsetrains of radio noise. Observations of this distinctive form of
lightning date from 1980 and have involved both ground-based and
satellite-based radio recording systems. The underlying intracloud lightning
discharges have been referred to as "Narrow Bipolar Pulses", "Narrow
Bipolar Events", and "Compact Intracloud Discharges". An important
discriminant for this species of radio emission is that, in the range above
~30 MHz, it consists of several microseconds of intense radio noise.
When the intracloud emission is viewed from a satellite, each radio
pulsetrain is received both from a direct lightning-to-satellite path, and
after some delay, from a path via ground. Thus one recording of the radio
emission, if of sufficient length, contains the "view" of the intracloud
emission from two different angles. One view is of radiation exiting the
emitter into the upper hemisphere, the other for radiation exiting into the
lower hemisphere. However, the propagation conditions are similar, except
that one path includes a ground reflection, while the other does not.
One would normally expect a stereoscopic double view of the "same"
emission process to provide two almost congruent time series, one delayed
from the other, and also differing due to the different propagation effects
along the two signal paths, namely, the ground reflection. We present
somewhat unexpected results on this matter, using recordings from the FORTE
satellite at a passband 118–141 MHz, with simultaneous data at 26–49 MHz. We
find that the 118–141 MHz pulsetrain's detailed time-dependence is
completely uncorrelated between the two views of the process. We examine
statistics of the 118–141 MHz pulsetrain's integrated power and show that
the power emitted into the lower hemisphere, on average, exceeds the power
emitted into the upper hemisphere. Finally, we examine statistical measures
of the amplitude distribution and show that the 118–141 MHz signal emitted
downward is slightly more dominated by discrete, temporally-narrow impulses
than is the signal emitted upward. |
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