Case studies of quasi-periodic VLF emissions and related ULF fluctuations of the magnetic field

Abstract:

Quasi-periodic (QP) VLF emissions are observed in the inner magnetosphere mostly on the day-side. These waves exhibit a periodic time modulation of the wave intensity that is possibly a result of the whistler-mode wave growth being periodically modulated by compressional ULF magnetic field pulsations. We have analyzed 50 QP events measured by the DEMETER satellite at altitudes of about 700 km to verify their generation mechanism.
The analyzed events have a modulation period between 15 s and 80 s, and they were observed during quiet geomagnetic conditions (Kp<3).
Magnetometers of the CARISMA system were used for monitoring the ULF magnetic field pulsations in a wide spatial range. We have found that ULF magnetic field pulsations in the Pc3 - Pc5 range are well correlated with the occurrence of the QP emissions with modulation periods between about 40 and 80 s. At the same time, increased fluxes of high-energy electrons (E > 30 keV) were observed by DEMETER and by the NOAA-17 satellite. We analyze possible links between these electrons, QP emissions, and ULF magnetic field pulsations.