Quasiperiodic Emissions and Related Particle Precipitation Bursts Observed by the DEMETER Spacecraft

Overview & Synopsis

Electromagnetic waves observed in the inner magnetosphere at frequencies between about 0.5 and 4 kHz sometimes exhibit a quasiperiodic (QP) time modulation of the wave intensity with modulation periods from tens of seconds up to a few minutes. Such waves are typically termed QP emissions and their origin is still not fully understood. We use a large set of more than 2,000 of these events identified in the low-altitude DEMETER spacecraft data to check for energetic electron flux variations matching the individual QP wave elements. Altogether, 7 such events are identified and their detailed analysis is performed. Energetic electron fluxes are found to be modulated primarily at energies lower than about 250 keV. While the waves may propagate unducted across L-shells, the energetic particles follow magnetic field lines from the interaction region down to the observation point. This is used to estimate the locations of anticipated generation regions to L-shells between about 4 and 6, and the respective source radial dimensions to about 0.6-1.2 Earth radii. The frequencies of the events are confined below half of the equatorial electron gyrofrequency in the determined source regions. Finally, it is shown that individual QP elements exhibit a fine inner structure corresponding to the wave bouncing between the hemispheres.