Statistical correlation of spectral broadening in VLF transmitter signal and low-frequency ionospheric turbulence from observation on DEMETER satellite

International audienceIn our earlier papers we have found the effectof VLF transmitter signal depression over epicenters of thelarge earthquakes from observation on the French DEMETERsatellite that can be considered as new method ofglobal diagnostics of seismic influence on the ionosphere.At present paper we investigate a possibility VLF signalionosphericturbulence interaction using additional characteristicof VLF signal-spectrum broadening. This characteristicis important for estimation of the interaction type: linearor nonlinear scattering. Our main results are the following:– There are two zones of increased spectrum broadening,which are centered near magnetic latitudes8=±10 and8=±40. Basing on the previous case study researchand ground ionosonde registrations, probably it is evidenceof nonlinear (active) scattering of VLF signal onthe ionospheric turbulence. However occurrence rateof spectrum broadening in the middle-latitude area ishigher than in the near-equatorial zone (15–20% incomparison with 100% in former area) that is probablycoincides with the rate of ionospheric turbulence.– From two years statistics of observation in the selected3 low-latitude regions and 1 middle-latitude region insidereception area of VLF signal from NWC transmitterwe find a correlation of spectrum broadening neitherwith ion-cyclotron noise (f =150–500 Hz), whichpossibly means poor representation of the turbulenceby the noise due to its mixture with natural ELF emission(which correlates with whistler), nor with magneticstorm activity.– We find rather evident correlation of ion-cyclotron frequencynoise, VLF signal depression and weak correlationof spectrum broadening with seismicity inthe middle-latitude region over Japan. But in thelow-latitude regions we do not find such a correlation.Statistical decrease of VLF signal supports ourprevious case study results. However rather weakspectrum broadening-seismicity statistical correlationmeans probably that passive scattering prevails uponnonlinear (active) one