Statistical correlation of spectral broadening in VLF transmitter signal and low-frequency ionospheric turbulence from observation on DEMETER satellite
Résumé
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 signalionospheric
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 latitudes8=±10 and
8=±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.
Origine : Publication financée par une institution
