Whistler Mode Quasiperiodic Emissions: Contrasting Van Allen Probes and DEMETER Occurrence Rates

F. Němec (1) , O. Santolík (2) , G. Hospodarsky (3) , M. Hajoš (1) , A. Demekhov (4) , W. Kurth (5) , Michel Parrot (6) , D. P Hartley

1 Faculty of Mathematics and Physics [Praha/Prague]
2 IAP - Institute of Atmospheric Physics [Prague]
3 Department of Physics and Astronomy [Iowa City]
4 Institute of Applied Physics of RAS
5 University of Iowa [Iowa City]
6 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace

Quasiperiodic emissions are magnetospheric whistler mode waves at frequencies between about 0.5 and 4 kHz which exhibit a nearly periodic time modulation of the wave intensity. We use large data sets of events observed by the Van Allen Probes in the equatorial region at larger radial distances and by the low-altitude DEMETER spacecraft. While Van Allen Probes observe the events at all local times and longitudes, DEMETER observations are limited nearly exclusively to the daytime and significantly less frequent at the longitudes of the South Atlantic Anomaly. Further, while the events observed by Van Allen Probes are smoothly distributed over seasons with only mild maxima in spring/autumn, DEMETER occurrence rate has a single pronounced minimum in July. The apparent inconsistency is explained by considering a nondipolar Earth's magnetic field and significant background wave intensities which in these cases prevent the quasiperiodic events from being identified in DEMETER data.

Domains: Sciences of the Universe [physics]

F. Němec, O. Santolík, G. Hospodarsky, M. Hajoš, A. Demekhov, et al.. Whistler Mode Quasiperiodic Emissions: Contrasting Van Allen Probes and DEMETER Occurrence Rates. Journal of Geophysical Research Space Physics, 2020, 125 (4), 9 p. ⟨10.1029/2020JA027918⟩. ⟨insu-02551712⟩