Solar Wind Entry Into Midtail Current Sheet via Low‐Latitude Mantle Under Dominant IMF By: ARTEMIS Observation

Abstract

AbstractIt is expected from global simulations that the low‐latitude mantle may be an important pathway for the solar wind entry into the tail current sheet when interplanetary magnetic field (IMF) By is dominant, which is different from the pathways for northward or southward IMF dominant conditions. To evaluate this pathway and the predicted plasma asymmetries between the southern and northern lobes resulting from the low‐latitude mantle, we analyze 222 current sheet crossing events observed in the midtail. Each of the events is selected to have the spacecraft observe both lobes within 20 min. For the majority of the events, the different north‐south asymmetries of the lobe density observed on the dawnside and duskside corresponding to different IMF By directions are consistent with the appearance of the low‐latitude mantle plasma. No significant north‐south asymmetry in the lobe magnetic field strength is found so that the density asymmetry also results in north‐south asymmetric lobe Alfvén speed. Within the tail current sheet, the cross‐tail profiles show that density can be higher, but temperatures and peak flow speed lower, near the flanks than near midnight. Magnitudes of these current sheet plasma parameters are found to positively correlate with the values of the asymmetric lobe parameters concurrently observed, indicating that the low‐latitude mantle can be a particle source for the current sheet. Also, the asymmetric lobe parameters are positively correlated with some solar wind parameters. These good correlations support the expectation that the pathway through the low‐latitude mantle becomes more important as the IMF By becomes more dominant.