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Atmospheric and ionospheric parameter variations inferred from sub-ionospheric seismo-electromagnetic VLF/LF observations. K. Schwingenschuh 1 , H. U. Eichelberger 1 , B. P. Besser 1 , G. Prattes 1 , M. Y. Boudjada 1 , G. Stangl 1 , D. Wolbang 2 ,

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Atmospheric and ionospheric parameter variations inferred from sub-ionospheric seismo-electromagnetic VLF/LF observations

K. Schwingenschuh1,H. U. Eichelberger1, B. P. Besser1, G. Prattes1, M. Y. Boudjada1,G. Stangl1,D. Wolbang2,

A. Rozhnoi3, M. Solovieva3, P. F. Biagi4, M. Friedrich5, H. Biernat1, and M. Hayakawa6,

1 IWF/ÖAW, Graz/Austria, 2 IGAM, KFU Graz, Graz/Austria,3 Institute of the Earth Physics, RAS, Moscow/Russia, 4 Department of Physics, University of Bari, Bari/Italy, 5 Institute of Communication Networks and Satellite Communications, Graz University of Technology, Graz/Austria, 6 The University of Electro-Communications (UEC), Advanced Wireless Communications Research Center, Chofu, Tokyo/Japan

Introduction

Sub-ionospheric waveguide and results

Future Outlook

  • Graz participates in seismo-electromagnetic (SEM) studies

  • Sub- and trans-ionospheric VLF radio links as well as Total Electron Content measurements are used

  • Graz is a part of an European VLF/LF SEM network and participates in the DEMETER SEM data analysis

  • The radio links are part of the ionospheric waveguide

  • Lithospheric-Atmospheric-Ionospheric coupling processes can disturb the waveguide parameter

  • The University of Technology in Graz has a long lasting experience in the study of sub- ionospheric wave propagation

Station network for combined invest-igations of local and mesoscale geophysical/ seismic phenomena, consisting of (i) VLF

only (red markers), (ii) VLF/LF (green), and (iii) South European Geo-magnetic Array (SEGMA) ULF (blue) receiving stations.

  • Numerical Modelling of the sub-ionospheric radio link between the receiver in Graz and the transmitter stations in Europe

  • Model input parameter: effective height of the ionospheric cavity, geometry of the radio path, conductivity profile

  • Expansion of the Ledinegg analytical model to understand the lithospheric-atmospheric-ionospheric coupling

  • The models can be used to solve the inverse problem of SEM, namely to derive seismo-electromagnetic parameters from VLF observations

Summary

  • The essential tool for VLF seismo-electromagnetic (SEM) studies is the radio link between transmitter and receiver

  • The parameters of the sub-ionospheric waveguide determine the properties of the received VLF signals

  • The main parameters of the waveguide are:

  • - effective height of the waveguide (60-90 km)

  • - distance transmitter-receiver

  • Terminator crossing parameter (angle,...)

  • Conductivity profile

  • Seismo-electromagnetic disturbances

Sketch of Lithosphere-Atmosphere-Ionosphere (LAI) coupling related to earthquakes and possible influences on satellite and ground based measurements.

During the DEMETER operational phase 2004-2010 we conducted complementary seismo-electromagnetic ground based ULF, TEC and VLF investigations. This combined satellite - ground based multi-parameter SEM approach provides the possibility to differentiate

seismic from non-seismic events.

References

  • E. Ledinegg, VLF mode conversion at terminator taking into account Earth’s curvature, Radio Science, 17, 879-887, 1982.

  • 2. G. Prattes, et al., Ground based and satellite communication channel influences and Ultra Low Frequency (ULF) remote sensing techniques. In: Proceedings of the 11th International Conference on Telecommunications (ConTEL 2011), Eds. Löschnigg, M., T. Plank, Graz University of Technology, Graz, 177-180, 2011.

  • 3. H. Zach, D. Kirchner und O. Laback, Numerische Simulation der Ausbreitung Elektromagnetischer Wellen im Frequenzbereich von 10-30 kHz, INW 7706, Institut für Nachrichtentechnik und Wellenausbreitung, Technische Universität Graz, 1977.

  • 4. S. Toledo-Redondo, M. Parrot, and A. Salinas, Variation of the first cut-off frequency of the Earth-ionosphere waveguide observed by DEMETER, Journal of Geophysical Research, 117, doi:10.1029/2011JA017400, 2012.

  • 5 D. Wolbang, et al., Seismo electro-magnetic parameter study of sub-ionospheric VLF radio links in Europe, Geophysical Research Abstracts, 14, EGU2012-761, 2012.

For sub-ionospheric VLF SEM studies performed in Graz the residual and the Terminator-Time (TT) methods is mainly used. (Wolbang 2012; Prattes 2011). The TT method is based on the anomalies of the VLF dawn and dusk amplitude depressions. The characteristic amplitude drop is well known and a result of new wave modes when the radio link crosses the terminator. Several years ago the University of Technology in Graz developed analytical (Ledinegg 1982) and numerical (Kirchner, Zach, Laback 1977) of the propagation of VLF radio waves in the sub-ionospheric wave guide.

VLF amplitude measurements for one year continuous operation on the path DHO-GRZ.

Map of the effective reflection height observed by DEMETER (see Toledo-Redondo 2012).


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