Additional attenuation of natural VLF electromagnetic waves observed by the DEMETER spacecraft resulting from preseismic activity

0395581 - ÚFA 2014 RIV US eng J - Článek v odborném periodiku
Píša, David - Němec, F. - Santolík, Ondřej - Parrot, M. - Rycroft, M.
Additional attenuation of natural VLF electromagnetic waves observed by the DEMETER spacecraft resulting from preseismic activity.
Journal of Geophysical Research-Space Physics. Roč. 118, č. 8 (2013), s. 5286-5295. ISSN 2169-9380. E-ISSN 2169-9402
Grant CEP: GA ČR(CZ) GAP209/11/2280; GA ČR GA205/09/1253
Grant ostatní: European Community Seventh Framework Programme (FP7/2007-2013),(XE) 262005; AV ČR(CZ) M100431206.
Institucionální podpora: RVO:68378289
Klíčová slova: DEMETER * VLF waves * preseismic activity * Earth-ionosphere waveguide
Kód oboru RIV: DG - Vědy o atmosféře, meteorologie
Impakt faktor: 3.440, rok: 2013
http://onlinelibrary.wiley.com/doi/10.1002/jgra.50469/abstract

We use VLF electromagnetic wave data measured by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite at an altitude of about 700 km to check for the presence of statistically significant changes of natural wave intensity (due to signals from lightning) related to preseismic activity. All the relevant data acquired by DEMETER during almost 6.5 years of the mission have been analyzed using a robust two-step data-processing schema. This enables us to compare data from the vicinity of about 8400 earthquakes with an unperturbed background distribution based on data collected during the whole DEMETER mission and to evaluate the statistical significance of the observed effects. We confirm previously reported results of a small but statistically significant decrease of the wave intensity (by 2 dB) at frequencies of about 1.7 kHz. The effect is observed for a few hours before the times of the main shocks; it occurs during the night. The effect is stronger between March and August, at higher latitudes and for the positions of hypocenters below the sea. We suggest an explanation based on changed properties of the lower boundary of the ionosphere, which leads to a decrease of the intensity of lightning-generated whistlers observed at the spacecraft altitude. This effect might result from a lowering of the ionosphere associated with an increase in the electrical conductivity of the lower troposphere due to an additional ionization of air molecules at the Earth’s surface prior to earthquakes.
Trvalý link: http://hdl.handle.net/11104/0223587