Modeling interactions of narrowband large amplitude whistler-mode waves with electrons in the solar wind inside ~.3 AU and at 1 AU using a particle tracing code

TL;DR

This study uses a 3D particle tracing code to model how large-amplitude narrowband whistler-mode waves interact with solar wind electrons, revealing rapid scattering and energization effects that challenge traditional quasi-linear theories.

Contribution

It introduces a comprehensive 3D simulation approach to analyze nonlinear electron interactions with whistler waves in the solar wind, highlighting effects overlooked by previous models.

Findings

Whistler waves cause rapid electron scattering and energization.

Nonlinear effects are significant, making quasi-linear models inadequate.

Scattering reduces electron heat flux and influences electron distribution.

Abstract

The discovery of large-amplitude narrowband whistler-mode waves at frequencies of tenths of the electron cyclotron frequency in large numbers both inside ~.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 and propagation angles from 0 to 180 degrees to the background magnetic field. Interactions with wave packets and single waves are both modeled based on observations at ~.3 AU and 1 AU. The simulations demonstrate the key role played by these waves in rapid scattering and energization of electrons. Results provide evidence for nonlinear effects, indicating that quasi-linear methods are not adequate for modeling the role of whistlers in the evolution of solar wind electrons. Strong scattering and energization for some initial energy and pitch angle ranges occurs for both counter-propagating and obliquely propagating waves. The strong scattering of strahl electrons counteracts the pitch angle narrowing due to conservation of the first adiabatic invariant as electrons propagate away 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.