Electron Scattering by Low-Frequency Whistler Waves at Earth's Bow Shock
Abstract
Electrons are accelerated to non-thermal energies at shocks in space and astrophysical environments. While Shock Drift Acceleration (SDA) has been considered a key process of electron acceleration at Earth's bow shock, it has also been recognized that SDA needs to be combined with an additional stochastic process to explain the observed power-law energy spectra. Here we show mildly energetic (~0.5 keV) electrons are locally scattered (and accelerated while being confined) by magnetosonic-whistler waves within the shock transition layer especially when the shock angle is large (θ Bn >~ 70°). When measured by the Magnetospheric MultiScale (MMS) mission at a high cadence, ~0.5 keV electron flux increased exponentially in the shock transition layer. However, the flux profile was not entirely smooth and the fluctuation showed temporal/spectral association with large-amplitude (δB/B ~ 0.3), low-frequency (<~0.1 Ω ce where Ω ce is the cyclotron frequency), obliquely-propagating (θ Bk ~ 30° - 60° where θ Bk is the angle between the wave vector and background magnetic field) whistler waves, indicating that the particles were interacting with the waves. Particle simulations demonstrate that the observed electron-whistler interaction is intrinsically non-linear and electrons can be scattered beyond 90° pitch angle.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSH21A..06O
- Keywords:
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- 7829 Kinetic waves and instabilities;
- SPACE PLASMA PHYSICS;
- 7845 Particle acceleration;
- SPACE PLASMA PHYSICS;
- 7846 Plasma energization;
- SPACE PLASMA PHYSICS;
- 7851 Shock waves;
- SPACE PLASMA PHYSICS