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| Titel |
Unstable whistlers and Bernstein waves within the front of supercritical perpendicular shocks |
| VerfasserIn |
Laurent Muschietti, Bertrand Lembège |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130434
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| Publikation (Nr.) |
 EGU/EGU2016-10690.pdf |
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| Zusammenfassung |
| In supercritical shocks a significant fraction of ions is reflected at the steep shock ramp and
carries a considerable amount of energy. The existence of reflected ions enables streaming
instabilities to develop which are excited by the relative drifts between the populations of
incoming ions, reflected ions, and electrons. The processes are fundamental to the
transformation of directed kinetic energy into thermal energy, a tenet of shock physics. We
model the particle distributions as a broad electron population and two ion populations,
namely a core and a beam (representing the reflected ions) in order to investigate the kinetic
instabilities possible under various wave propagation angles. Recently, assuming the ion
beam is directed along the shock normal at 90∘ to the magnetic field Bo, we analyzed the
linear dispersion properties by computing the full electromagnetic dielectric tensor
[Muschietti and Lembege, AGU Fall meeting 2015]. Three types of waves were
shown to be unstable: (1) Oblique whistlers with wavelengths about the ion inertia
length which propagate toward upstream at angles about 50∘ to the magnetic field.
Frequencies are a few times the lower-hybrid. The waves share many similarities
to the obliquely propagating whistlers measured in detail by Polar [Hull et al.,
JGR 117, 2012]. (2) Quasi-perpendicular whistlers with wavelength covering a
fraction of the electron inertia length which propagate toward downstream at angles
larger than 80∘ to Bo. Frequencies are close to the lower-hybrid. (3) Bernstein
waves with wavelengths close to the electron gyroradius which propagate toward
upstream at angles within 5∘ of perpendicular to the magnetic field. Frequencies
are close to the electron cyclotron. The waves have similarities to those reported
by Wind and Stereo [Breneman et al., JGR 118, 2013; Wilson et al., JGR 115,
2010].
We will present electromagnetic 1D3V PIC simulations with predetermined propagation
angles which illustrate the three types of waves. Power spectra, waveforms, polarizations,
and hodograms are shown and discussed in light of the dispersion results. Phase
spaces of each population are examined to evidence energy transfer and particle
acceleration. |
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