Properties of low‐latitude mantle plasma in the Earth's magnetotail: ARTEMIS observations and global MHD predictions

Abstract

AbstractThe Earth's plasma mantle is one of the major suppliers of particles for the plasma sheet. To understand its plasma characteristics, spatial distributions, and dependencies on interplanetary magnetic field (IMF) direction, we statistically analyzed the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) observations in the low‐latitude magnetotail (~10 RE above and below the current sheet) and investigated the predictions from global Block Adaptive Tree Solar wind‐Roe‐Upwind Scheme MHD simulations. The mantle plasma flows tailward along magnetic field lines (~50–200 km/s) and at the same time drifts toward midnight and toward the current sheet. The mantle plasma has similar temperature (~0.05–0.2 keV) to the magnetosheath plasma but has lower density (~0.1–1 cm−3). The mantle appearance is dawn‐dusk asymmetric depending mainly on the IMF By direction. The occurrence rates, density, and V|| all decrease with decreasing |Y|. This density cross‐tail profile suggests that the low‐latitude mantle plasma mainly comes from the magnetosheath entering through the tail magnetopause along the open field lines. Density is highly and positively correlated with V||. These observations are qualitatively consistent with the MHD results. The simulations indicate that as IMF By becomes dominant, the source locations at the magnetopause for the mantle move to lower latitudes and become dawn‐dusk asymmetric, and the tail cross section also becomes distorted with the magnetopause shape elongating and the current sheet tilting significantly. Degrees of these changes also vary with the downtail distances and IMF Bz direction. The source location change leads to the dawn‐dusk asymmetric mantle appearance. The tail cross‐section change alters the distance from the sources to the current sheet and thus the resulting mantle density distributions just outside the plasma sheet.