Abstract
Abstract The Earth’s bow shock is known to produce non-thermal electrons which are generally observed as a ‘spike’ in their flux profile. Here, in this paper, we present an analysis of electron and whistler wave properties for a quasi-perpendicular shock crossing that is supercritical, but subcritical to the so-called whistler critical Mach number, M crit w , above which whistler waves cannot propagate upstream. We have found that the amplitudes of whistler waves increased exponentially as a function of time prior to the shock encounter, while the suprathermal (>2 keV) electron flux similarly increased with time, although with differing e-folding time scales. Comparison of the electron energy spectrum measured within the ramp with predictions from diffusive shock acceleration theory was poor, but the variation of pitch angle distribution showed scattering of non-thermal electrons in the upstream region. While not finding a specific mechanism to account for the electron diffusion, we suggest that the whistlers seen probably account for the differences observed between this ‘gradual’ event and the ‘spike’ events seen at shocks with no upstream whistlers.
Highlights
Energetic electrons with energies of more than 20 keV have been observed at and near the Earth’s bow shock (e.g., Fan et al, 1964; Frank and Van Allen, 1964; Anderson, 1969; Vandas, 1989)
We have found that the amplitudes of whistler waves increased exponentially as a function of time prior to the shock encounter, while the suprathermal (>2 keV) electron flux increased with time, with differing e-folding time scales
Since larger electron flux can be found on the interplanetary magnetic field (IMF) tangent to the bow shock (e.g., Anderson et al, 1979; Kasaba et al, 2000), electrons are considered to be accelerated in the quasi-perpendicular region where the shock angle θBn is larger than 45◦
Summary
Energetic electrons with energies of more than 20 keV have been observed at and near the Earth’s bow shock (e.g., Fan et al, 1964; Frank and Van Allen, 1964; Anderson, 1969; Vandas, 1989). The Earth’s bow shock is known to produce non-thermal electrons which are generally observed as a ‘spike’ in their flux profile. In this paper, we present an analysis of electron and whistler wave properties for a quasi-perpendicular shock crossing that is supercritical, but subcritical to the so-called whistler critical Mach number, Mwcrit, above which whistler waves cannot propagate upstream.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
