A Multi-Scale Particle-in-Cell Simulation of Plasma Dynamics from
Magnetotail Reconnection to the Inner Magnetosphere
Abstract
During magnetospheric substorms, plasma from magnetic reconnection in
the magnetotail is thought to reach the inner magnetosphere and form a
partial ring current. We simulate this process using a fully kinetic 3D
particle-in-cell (PIC) numerical code along with a global
magnetohydrodynamics (MHD) model. The PIC simulation extends from the
solar wind outside the bow shock to beyond the reconnection region in
the tail, while the MHD code extends much further and is run for nominal
solar wind parameters and a southward interplanetary magnetic field. By
the end of the PIC calculation, ions and electrons from the tail
reconnection reach the inner magnetosphere and form a partial ring
current and diamagnetic current. The primary source of particles to the
inner magnetosphere is bursty bulk flows (BBFs) that originate from a
complex pattern of reconnection in the near-Earth magnetotail at
xGSM=-18 RE to -30 RE. Most ion acceleration occurs in this region,
gaining from 10 to 50 keV as they traverse the sites of active
reconnection. Electrons jet away from the reconnection region much
faster than the ions, setting up an ambipolar electric field allowing
the ions to catch up after approximately 10 ion inertial lengths. The
initial energy flux in the BBFs is mainly kinetic energy flux from the
ions, but as they move earthward, the energy flux changes to enthalpy
flux at the ring current. The power delivered from the tail reconnection
in the simulation to the inner magnetosphere is >2x1011 W,
which is consistent with observations.