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| Titel |
On the generation mechanism of terminator times in subionospheric VLF/LF propagation and its possible application to seismogenic effects |
| VerfasserIn |
M. Yoshida, T. Yamauchi, T. Horie, M. Hayakawa |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 8, no. 1 ; Nr. 8, no. 1 (2008-02-25), S.129-134 |
| Datensatznummer |
250005327
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| Publikation (Nr.) |
 copernicus.org/nhess-8-129-2008.pdf |
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| Zusammenfassung |
| The signals from VLF/LF transmitters are known to propagate in the
Earth-ionosphere waveguide, so that the subionospheric propagation
characteristics are very sensitive to the condition of the lower ionosphere.
We know that there appear the terminator times just around the sunrise and
sunset in the diurnal variation of subionospheric VLF/LF signal (amplitude
and phase). These terminator times are found to shift significantly just
around an earthquake, which enables us to infer the change in the ionosphere
during the earthquake. In this paper we try to understand the physical
mechanism on the generation of those terminator times for relatively short
propagation path (less than 2000 km) by means of wave-hop method. It is
found that the lowering of the ionosphere boundary during an earthquake
decreases the path length of the sky wave and this alters the interference
condition of this wave with the ground wave, which lead to an appearance of
terminator times as the destructive interference between the ground and sky
waves. Finally, we suggest a possible use of terminator time shifts to
investigate the lower ionospheric plasma changes during the earthquakes. |
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