Effect of IMF B-y on the Entry of Solar Wind Ions Into the Near-Earth Tail Lobe: Global Hybrid Simulation and MMS Observation

Abstract

Global simulations predict that the low-latitude mantle may be an important pathway for the solar wind entry into the tail magnetosphere close to the current sheet when interplanetary magnetic field (IMF) B-y dominates over IMF B-z. To evaluate this entry mechanism in the near-Earth tail (X similar to -10--20 R-E), we investigate the predictions from 3D global hybrid simulations as well as in situ observations by magnetospheric multiscale (MMS) spacecraft. The simulations predict that the low-latitude mantle plasma can appear in the near-Earth tail lobe extending inward approximately 5 R-E from the flank magnetopause. The low-latitude mantle plasma appears in the dawnside northern lobe and duskside southern lobe during positive IMF B-y, while the opposite asymmetry is seen during negative IMF B-y. After a change in the IMF B-y direction arriving at the bow shock nose, it takes another similar to 15-30 min for the asymmetry to completely reverse to the opposite sense in the near-Earth tail. We present six MMS events in the tail lobe showing that the existence and absence of the low-latitude mantle plasma is consistent with the predicted asymmetries. Statistical analysis of 5 years of MMS observations shows that the dependencies of the magnitudes of the lobe densities and tailward field-aligned flow speeds on the IMF B-y directions are consistent with the predicted contributions from the low-latitude mantle plasma in the expected lobe regions.