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| Titel |
Detection of ionospheric perturbations associated with Japanese earthquakes on the basis of reception of LF transmitter signals on the satellite DEMETER |
| VerfasserIn |
F. Muto, M. Yoshida, T. Horie, M. Hayakawa, M. Parrot, O. A. Molchanov |
| 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 (2008-02-26), S.135-141 |
| Datensatznummer |
250005328
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| Publikation (Nr.) |
 copernicus.org/nhess-8-135-2008.pdf |
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| Zusammenfassung |
| There have been recently reported a lot of electromagnetic phenomena
associated with earthquakes (EQs). Among these, the ground-based reception
of subionospheric waves from VLF/LF transmitters, is recognized as a
promising tool to investigate the ionospheric perturbations associated with
EQs. This paper deals with the corresponding whistler-mode signals in the
upper ionosphere from those VLF/LF transmitters, which is the counterpart of
subionospheric signals. The whistler-mode VLF/LF transmitter signals are
detected on board the French satellite, DEMETER launched on 29 June 2004.
We have chosen several large Japanese EQs including the Miyagi-oki EQ (16
August 2005; M=7.2, depth=36 km), and the target transmitter is a Japanese
LF transmitter (JJY) whose transmitter frequency is 40 kHz. Due to large
longitudinal separation of each satellite orbit (2500 km), we have to adopt
a statistical analysis over a rather long period (such as 3 weeks or one
month) to have reliable data set. By analyzing the spatial distribution of
JJY signal intensity (in the form of signal to noise ratio SNR) during a
period of 4 months including the Miyagi-oki EQ, we have found significant
changes in the intensity; generally the SNR is significantly depleted before
the EQ, which is considered to be a precursory ionospheric signature of the
EQ. This abnormal effect is reasonably explained in terms of either (1)
enhanced absorption of whistler-mode LF signals in the lower ionosphere due
to the lowering of the lower ionosphere, or (2) nonlinear wave-wave
scattering. Finally, this analysis suggests an important role of satellite
observation in the study of lithosphere-atmosphere-ionosphere coupling. |
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