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| Titel |
Anomalous effect in Schumann resonance phenomena observed in Japan, possibly associated with the Chi-chi earthquake in Taiwan |
| VerfasserIn |
M. Hayakawa, K. Ohta, A. P. Nickolaenko, Y. Ando |
| 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 ; 23, no. 4 ; Nr. 23, no. 4 (2005-06-03), S.1335-1346 |
| Datensatznummer |
250015227
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| Publikation (Nr.) |
 copernicus.org/angeo-23-1335-2005.pdf |
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| Zusammenfassung |
| The Schumann resonance phenomenon has been monitored at Nakatsugawa (near Nagoya)
in Japan since the beginning of 1999, and due to the occurance of a severe
earthquake (so-called Chi-chi earthquake) on 21 September 1999 in Taiwan we
have examined our Schumann resonance data at Nakatsugawa during the entire
year of 1999. We have found a very anomalous effect in the Schumann
resonance, possibly associated with two large land earthquakes (one is the
Chi-chi earthquake and another one on 2 November 1999 (Chia-yi earthquake)
with a magnitude again greater than 6.0). Conspicuous effects are observed for
the larger Chi-chi earthquake, so that we summarize the characteristics for
this event. The anomaly is characterized mainly by the unusual increase in
amplitude of the fourth Schumann resonance mode and a significant frequency
shift of its peak frequency (~1.0Hz) from the conventional value on
the By magnetic field component which is sensitive to the waves
propagating in the NS meridian plane. Anomalous Schumann resonance signals
appeared from about one week to a few days before the main shock. Secondly,
the goniometric estimation of the arrival angle of the anomalous signal is found
to coincide with the Taiwan azimuth (the unresolved dual direction indicates
toward South America). Also, the pulsed signals, such as the Q-bursts, were
simultaneously observed with the "carrier" frequency around the peak
frequency of the fourth Schumann resonance mode. The anomaly for the second event
for the Chia-yi earthquake on 2 November had much in common. But, most likely due to
a small magnitude, the anomaly appears one day before and lasts
until one day after the main shock, with the enhancement at the fourth
Schumann resonance mode being smaller in amplitude than the case of the
Chi-chi earthquake. Yet, the other characteristics, including the goniometric
direction finding result, frequency shift, etc., are nearly the same. Although
the emphasis of the present study is made on experimental aspects, a possible
generation mechanism for this anomaly is discussed in terms of the ELF radio
wave scattered by a conducting disturbance, which is likely to take place in
the middle atmosphere over Taiwan. Model computations show that the South
American thunderstorms (Amazon basin) play the leading role in maintaining
radio signals, leading to the anomaly in the Schumann resonance. |
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