15:30 〜 16:30
[S11-P-04] Clarification of the mechanism of VLF radiation intensity reduction before earthquakes observed by DEMETER and WWLLN data
Statistical observations by DEMETER have shown that a decrease of the VLF EM wave intensity around 1.7 kHz the cut-off frequency of the Earth's-Ionosphere guide occurs a few hours before an EQ. It is thought that this effect arises from a disturbance in the D-region of the ionosphere.
To further investigate this phenomenon we have analyzed whistler signals observed on DEMETER data using also lightning data from the WWLLN network. Whistlers that travel through the ionosphere up to the satellite should indeed be good tracers of possible low altitude ionospheric disturbances that may, in particular, modify the absorption rate of the propagating EM waves.
Whistler measurements obtained on board DEMETER in March 2010 before the Sumatra EQ have been compared with similar observations performed before and after the EQ but during seismically quiet periods. Initial results are consistent with an increase in the whistler wave absorption up to a few dB a few hours prior to EQ that could result from an enhancement of about 10-15% of the electron density in the lower ionosphere.
In this presentation we report the data processing methodology based on the combined use of in-orbit (DEMETER) and ground-based (WWLLN) measurements and initial quantitative outcomes of the deduced ionosphere variations. Further studies are required to build the necessary statistical knowledge of the phenomenon and identify the spatial scales of the ionosphere disturbances.
To further investigate this phenomenon we have analyzed whistler signals observed on DEMETER data using also lightning data from the WWLLN network. Whistlers that travel through the ionosphere up to the satellite should indeed be good tracers of possible low altitude ionospheric disturbances that may, in particular, modify the absorption rate of the propagating EM waves.
Whistler measurements obtained on board DEMETER in March 2010 before the Sumatra EQ have been compared with similar observations performed before and after the EQ but during seismically quiet periods. Initial results are consistent with an increase in the whistler wave absorption up to a few dB a few hours prior to EQ that could result from an enhancement of about 10-15% of the electron density in the lower ionosphere.
In this presentation we report the data processing methodology based on the combined use of in-orbit (DEMETER) and ground-based (WWLLN) measurements and initial quantitative outcomes of the deduced ionosphere variations. Further studies are required to build the necessary statistical knowledge of the phenomenon and identify the spatial scales of the ionosphere disturbances.