Particle dynamics in the reconnecting heliospheric current sheet: Solar wind data versus three-dimensional particle-in-cell simulations

Abstract

In this paper, we apply an assumption of the reconnecting heliospheric current sheet (HCS) for explanation of some contradictory results in the experimental detection of the sector boundaries (SBs) from the interplanetary magnetic field and electron pitch-angle measurements. Trajectories, densities, velocity, and pitch-angle distributions of particles accelerated by a super-Dreicer electric field are investigated with 2.5D full kinetic particle-in-cell approach in the HCS assumed to undergo a slow magnetic reconnection process with magnetic field configurations deduced from the solar wind observations. This approach reveals that during motion in a current sheet both kinds of particles, electrons and protons, are to be separated, either fully or partially, with respect to its midplane that can lead to their ejection to the opposite semiplanes that was also observed during the HCS crossings. This separation is found to form Hall's currents and polarization electric field across the current sheet, which distribution over the current sheets allows us to reproduce the magnitudes and temporal profiles of proton and ion velocities measured across the SB (current sheet midplane). This separation process, in turn, divides both kinds of particles on "transit" and "bounced" ones depending on a side of the current sheet where they enter it and where they are supposed to be ejected. The transit and bounced protons reproduce rather closely the measured distributions of proton/ion densities about the current sheet midplane with a larger maximum occurring at the heliospheric SB to be formed by the bounced protons and the other two smaller maximums on both sides from the central one to be formed by "transit" protons. The observed electron distributions of density and energy before and after sector boundary crossings are found to fit the simulated ones for electrons accelerated in a current sheet revealing a sharp increase of density from one side from the HCS boundary and a depression from the other side. The transit electrons are shown to gain energies up to ten of keV while the bounced ones gain only a few tens of eV as often measured in the HCS with a single crossing that results in the bump-in-tail electron distributions leading to Langmuir turbulence. The bounced electrons are shown to be responsible for the increased density of electrons detected at some distance from the HCS boundary (midplane) with the horse shoe-like or medallion- (or locket)-type distributions in pitch angles with the distance, at which electrons turn away from the HCS, being dependent on a magnitude of the guiding magnetic field. © 2012. The American Astronomical Society. All rights reserved..