Particle orbits at the magnetopause: Kelvin-Helmholtz induced trapping

TL;DR

This study investigates how Kelvin-Helmholtz instability at the magnetopause influences charged particle orbits, revealing complex trapping and energy gain mechanisms through detailed simulations of magnetic reconnection and particle dynamics.

Contribution

It introduces a detailed analysis of particle trajectories in DMLR configurations, highlighting the effects of magnetic curvature drifts and local cavities on particle trapping and energization.

Findings

Particles experience complex, temporarily trapped trajectories.

Magnetic curvature drifts dominate particle motion.

Local cavities facilitate particle energy gain.

Abstract

The Kelvin-Helmholtz instability (KHI) is a known mechanism for penetration of solar wind matter into the magnetosphere. Using three-dimensional, resistive magnetohydrodynamic simulations, the double mid-latitude reconnection (DMLR) process was shown to efficiently exchange solar wind matter into the magnetosphere, through mixing and reconnection. Here, we compute test particle orbits through DMLR configurations. In the instantaneous electromagnetic fields, charged particle trajectories are integrated using the guiding centre approximation. The mechanisms involved in the electron particle orbits and their kinetic energy evolutions are studied in detail, to identify specific signatures of the DMLR through particle characteristics. The charged particle orbits are influenced mainly by magnetic curvature drifts. We identify complex, temporarily trapped, trajectories where the combined electric field and (reconnected) magnetic field variations realize local cavities where particles gain energy before escaping. By comparing the orbits in strongly deformed fields due to the KHI development, with the textbook mirror-drift orbits resulting from our initial configuration, we identify effects due to current sheets formed in the DMLR process. We do this in various representative stages during the DMLR development.