Observation of ionospherically reflected quasiperiodic emissions by the DEMETER spacecraft

Abstract

Quasiperiodic (QP) electromagnetic emissions are whistler mode waves at typical frequencies of a few kHz characterized by a periodic time modulation of their intensity. The DEMETER spacecraft observed events where the QP emissions exhibit a sudden change in the wave vector and Poynting vector directions. The change happens in a short interval of latitudes. We explain this behavior by ionospheric reflection and present a ray‐tracing simulation which matches resulting wave vector directions. We also attempt to locate the source region of these emissions and conclude that they are most probably generated at the inner boundary of the plasmapause which also acts as a guide during the propagation of the QP emissions.

Simultaneous Observations of ELF/VLF Rising‐Tone Quasiperiodic Waves and Energetic Electron Precipitations in the High‐Latitude Upper Ionosphere

“…This result is consistent with ray tracing result shown in Fig. 3 of Hanzelka et al (2017), where the guiding effect of the plasmapause is proposed to enable QP propagating downward from the magnetosphere and refract towards the lower L shell region.…”

“…It is well known that the plasmasphere (the lower part of the inner magnetosphere) can overlap with the ionosphere in the high‐latitude region at various scales depending on the geomagnetically disturbed conditions. Previous studies show that most QP waves appear in the vicinity of the plasmapause boundary where there is a density gradient, and some studies (i.e., Hanzelka et al, 2017; Kimura, 1974) suggest that the generation source of QP waves depends on the position of plasmapause, which acts as a waveguide enabling QP waves to propagate downward into the ionosphere. Němec et al (2013) further interpreted that because of the guiding effects of the plasmapause, the QP waves at lower altitudes could deviate in the direction of the lower L shells (see Fig.…”

“…Previous studies revealed that QP waves mostly appear near the inner boundary side of the plasmapause in the high‐latitude ionosphere region. Theoretical simulations (i.e., Hanzelka et al, 2017) also support the idea that the plasmapause could act as a guide enabling QP waves to propagate downward to the lower‐altitude regions. Previous studies (Němec et al, 2013, Němec, Hospodarsky, et al, 2016,Němec, Bezděková, et al, 2016; Titova et al, 2015) also reported simultaneous conjugation observations of QP waves in both the upper ionosphere and the inner magnetosphere, suggesting that their source is located in the equatorial region near the plasmapause boundary.…”

Quasiperiodic ELF/VLF Emissions Detected Onboard the DEMETER Spacecraft: Theoretical Analysis and Comparison With Observations

“…This model is based on a self‐consistent set of equations of the quasi‐linear plasma theory for the distribution function of energetic electrons F ( μ , v , t ) and whistler wave spectral energy density ε ( ω , t ): where is the equatorial pitch angle, v is the electron velocity, T b is the bounce‐oscillation period, D is the coefficient of pitch‐angle diffusion, J describes the effective source of energetic electrons, Γ is the one‐hop gain of whistler waves on the pass between conjugate ionospheres, T gr is the period of wave‐packet bounce oscillations between conjugate ionospheres, and R is the effective reflection coefficient describing wave energy losses. Details of the reflection process of the QP emissions have been described by Hanzelka et al ().…”

“…where = sin 2 Θ L , Θ L is the equatorial pitch angle, v is the electron velocity, T b is the bounce-oscillation period, D is the coefficient of pitch-angle diffusion, J describes the effective source of energetic electrons, is the one-hop gain of whistler waves on the pass between conjugate ionospheres, T gr is the period of wave-packet bounce oscillations between conjugate ionospheres, and R is the effective reflection coefficient describing wave energy losses. Details of the reflection process of the QP emissions have been described by Hanzelka et al (2017). (1) and (2) are obtained by averaging the basic quasi-linear equations over particle bounce oscillations between the mirror points and wave-packet oscillations between conjugate ionospheres, as well as over the cross section of the interaction region.…”