Abstract
Abstract. We present results of noon–midnight meridional plane global hybrid-Vlasov simulations of the magnetotail ion dynamics under a steady southward interplanetary magnetic field using the Vlasiator model. The simulation results show magnetotail reconnection and formation of earthward and tailward fast plasma outflows. The hybrid-Vlasov approach allows us to study ion velocity distribution functions (VDFs) that are self-consistently formed during the magnetotail evolution. We examine the VDFs collected by virtual detectors placed along the equatorial magnetotail within earthward and tailward outflows and around the quasi-steady X line formed in the magnetotail at X≈-14RE. This allows us to follow the evolution of VDFs during earthward and tailward motion of reconnected flux tubes as well as study signatures of unmagnetized ion motion in the weak magnetic field near the X line. The VDFs indicate actions of Fermi-type and betatron acceleration mechanisms, ion acceleration by the reconnection electric field, and Speiser-type motion of ions near the X line. The simulated VDFs are compared and show good agreement with VDFs observed in the magnetotail by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. We find that the VDFs become more gyrotropic but retain transverse anisotropy and counterstreaming ion beams when being convected earthward. The presented global hybrid-Vlasov simulation results are valuable for understanding physical processes of ion acceleration during magnetotail reconnection, interpretation of in situ observations, and for future mission development by setting requirements on pitch angle and energy resolution of upcoming instruments.
Highlights
According to the near-Earth neutral line model (e.g., Baker et al, 1996), magnetotail reconnection occurs at geocentric distances of 20–30 Earth radii (RE) (Nagai et al, 1998, 2005) and may operate in the fast, impulsive regime as well as in the quasi-steady regime
We present a comprehensive analysis of the obtained ion velocity distribution functions (VDFs) within the tail
We have examined the VDFs that were observed by virtual detectors placed in the vicinity of the main X point and within earthward and tailward reconnection outflows
Summary
According to the near-Earth neutral line model (e.g., Baker et al, 1996), magnetotail reconnection occurs at geocentric distances of 20–30 Earth radii (RE) (Nagai et al, 1998, 2005) and may operate in the fast, impulsive regime as well as in the quasi-steady regime. Hoshino et al (1998) studied ion VDFs (in the context of this paper, we will further focus on the ion kinetics) observed by the Geotail satellite and compared them with results of 2D PIC simulations They showed that the ion VDFs near and in the reconnection region are non-Maxwellian and include counterstreaming beams and nongyrotropic and thermalized populations. A realistic model with the dipole field at the earthward side of the simulation is needed to accurately describe the ion kinetics within the plasma sheet It is worth noting, that particle kinetics during magnetic reconnection is extremely complex. We aim to understand the tail VDFs in terms of reconnection processes in a self-consistent ion-kinetic setup using such a large simulation domain that it covers the reconnection regions and the outflows while using a realistically sized Earth dipole.
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