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Titel |
Day-time variations of foE and foF2 connected to earthquakes |
VerfasserIn |
E. V. Liperovskaya, V. V. Bogdanov, P.-F. Biagi, C.-V. Meister, V. A. Liperovsky, D. H. H. Hoffmann |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250033637
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Zusammenfassung |
In the present work, disturbances of the characteristic frequencies foE and foF2 of the
ionosphere are studied to find out if they may be considered as possible earthquake
precursors. These frequencies are proportional to the square root of the maximal electron
density in the E- and F-layer of the ionosphere, respectively. The statistical analysis of the
frequencies foE and foF2 is performed using data of the vertical sounding radar station
Tashkent (latitude φ = 41.3o N, longitude λ = 69.6o E), obtained from 1964 until 1996
every hour. Experimental observations averaged over mid-day hours from 11 till 17 h LT are
considered on the background of seasonal, geomagnetic, 11-years and 27-days Solar
variations. Special normalized parameters E and F are introduced, which represent the
almost seasonal-independent part of foE and foF2. Days with higher Solar (Wolf
number > 100) and geomagnetic (ΣKp > 25) disturbances are excluded from the
analysis. It is shown that, for the whole data massive, that means considering all
days studied, no correlations between the normalized parameters of the E- and
F-layer are found (correlation coefficient 0.05). Further, the superimposed epoches
method is used to determine the temporal dependence of the parameters of the E-
and F-layers. It is found that the normalized parameters of both layers increase
one day before the earthquakes, and then decrease before the seismic shock. The
decrease is obtained for earthquakes occurring at distances smaller than 1500 km from
the ionospheric radar station and having a depth of the epicenter not larger than
60 km. The increase of foE occurs for earthquakes with magnitudes M > 4.5,
and the increase of foF2 is obtained for events with M > 5. The reliability of the
effect is larger than 95 %. Possible physical processes causing the phenomenon are
discussed. |
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