Abstract
Abstract. In our earlier papers we have found the effect of VLF transmitter signal depression over epicenters of the large earthquakes from observation on the French DEMETER satellite that can be considered as new method of global diagnostics of seismic influence on the ionosphere. At present paper we investigate a possibility VLF signal-ionospheric turbulence interaction using additional characteristic of VLF signal-spectrum broadening. This characteristic is important for estimation of the interaction type: linear or nonlinear scattering. Our main results are the following: – There are two zones of increased spectrum broadening, which are centered near magnetic latitudes Φ=±10° and Φ=±40°. Basing on the previous case study research and ground ionosonde registrations, probably it is evidence of nonlinear (active) scattering of VLF signal on the ionospheric turbulence. However occurrence rate of spectrum broadening in the middle-latitude area is higher than in the near-equatorial zone (~15–20% in comparison with ~100% in former area) that is probably coincides with the rate of ionospheric turbulence. – From two years statistics of observation in the selected 3 low-latitude regions and 1 middle-latitude region inside reception area of VLF signal from NWC transmitter we find a correlation of spectrum broadening neither with ion-cyclotron noise (f=150–500 Hz), which possibly means poor representation of the turbulence by the noise due to its mixture with natural ELF emission (which correlates with whistler), nor with magnetic storm activity. – We find rather evident correlation of ion-cyclotron frequency noise, VLF signal depression and weak correlation of spectrum broadening with seismicity in the middle-latitude region over Japan. But in the low-latitude regions we do not find such a correlation. Statistical decrease of VLF signal supports our previous case study results. However rather weak spectrum broadening-seismicity statistical correlation means probably that passive scattering prevails upon nonlinear (active) one.
Highlights
In our earlier papers we have found the effect of VLF transmitter signal depression over epicenters of the large earthquakes from observation on the French DEMETER satellite that can be considered as new method of global diagnostics of seismic influence on the ionosphere (Molchanov et al, 2006; Rozhnoi et al, 2007)
– There are two zones of increased spectrum broadening, which are centered near magnetic latitudes =±10◦ and =±40◦
In our earlier papers we have found the effect of VLF transmitter signal depression over epicenters of the large earthquakes from observation on the French DEMETER satellite that can be considered as new method of global diagnostics of seismic influence on the ionosphere (Molchanov et al, 2006; Rozhnoi et al, 2007)
Summary
In our earlier papers we have found the effect of VLF transmitter signal depression over epicenters of the large earthquakes from observation on the French DEMETER satellite that can be considered as new method of global diagnostics of seismic influence on the ionosphere (Molchanov et al, 2006; Rozhnoi et al, 2007) In particular it was shown rather reliable decrease of Australian NWC transmitter signal amplitude several days before and after three large earthquakes (magnitude M>6) in Japan region both from satellite and simultaneously on the ground observation (Rozhnoi et al, 2007). It was found that aside of high-latitude regions (magnetic latitudes | |>60◦) the regular ionospheric turbulence intensification existed near Equatorial Anomaly of plasma density (magnetic latitudes =±10–15◦) and in the middlelatitude areas ( =±30–40◦), and it was supposed that just these areas were vulnerable for seismic influence and gave input in statistical estimation. This anomalous SB phenomenon was observed in many satellite observations both in high-latitude areas (Bell et al, 1983; Titova et al, 1984) and the middle latitudes (Tanaka et al, 1987) and it was interpreted by mechanism of three-wave interaction of VLF waves and ionospheric turbulence
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