Abstract
Abstract The discovery of large amplitude narrowband whistler-mode waves at frequencies of tenths of the electron cyclotron frequency in large numbers both inside ∼0.3 au and at ∼1 au provides an answer to longstanding questions about scattering and energization of solar wind electrons. The waves can have rapid nonlinear interactions with electrons over a broad energy range. Counter propagation between electrons and waves is not required for resonance with the obliquely propagating waves in contrast to the case for parallel propagation. Using a full 3D particle tracing code, we have examined interactions of electrons with energies from 0 eV to 2 keV with whistler-mode waves with amplitudes of 20 mV m−1 and propagation angles from 0° to 180° to the background magnetic field. Interactions with wave packets and single waves are both modeled based on observations at ∼0.3 au and 1 au. A test particle simulation approach allows us to examine the particle motion in detail, which reveals kinetic effects of resonant interactions. The simulations demonstrate the key role played by these waves in rapid scattering and energization of electrons. Strong scattering and energization for some initial energy and pitch angle ranges occurs for both counter-propagating and obliquely propagating waves. Strong scattering of strahl electrons counteracts the pitch angle narrowing due to conservation of the first adiabatic invariant as electrons propagate from the Sun into regions of smaller magnetic field. Scattering also produces the hotter isotropic halo. The concomitant limiting of the electron heat flux is also relevant in other astrophysical settings.
Highlights
Many researchers have studied the evolution of solar wind electron distributions as they propagate away from the Sun
If only adiabatic effects are included, the field-aligned suprathermal strahl electrons would narrow in pitch angle with distance from the Sun, losing perpendicular energy as the magnetic field decreases to conserve the first adiabatic invariant
Because the strahl electrons carry the bulk of the heat flux, many studies are framed as determining the mechanisms that control the heat flux (Gary et al, 1994; Bale et al, 2013; Halekas et al, 2020b)
Summary
Until recently most theoretical studies focused on waves propagating parallel to the solar wind magnetic field. For these waves, the resonance condition, ω − k$⃗ ∙ v$$$(⃗ = nΩ(, can only be satisfied if the whistler-mode waves propagate sunward, opposite to the bulk of the electrons (Vocks et al, 2005; Gary and Saito, 2007). We focus on the interaction of solar wind electrons with whistler-mode waves using a 3d particle tracing code with initial electron distributions and whistler properties based on those observed both at ~1 AU and inside ~.3.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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.
