Dawn-Dusk Asymmetries of Solar-Wind-Magnetosphere Coupling in the Earth's Midtail

Solar-wind-magnetosphere coupling causes plasma exchange across the magnetopause. Using ARTEMIS observations, we investigated dawn-dusk asymmetries and responsible coupling processes for two distinct populations in the midtail (r similar to 60 R-E): (1) mantle plasma resulting from magnetosheath plasma coming through the open magnetopause and (2) bursty hot electron enhancements (HEEs) in the magnetosheath resulting from magnetosphere electrons coming out with transient magnetopause deformation. Mantle plasma appears more frequently in the postmidnight (premidnight) sector above the current sheet when the IMF B-y is positive (negative). Good agreement between the observations and global MHD simulations indicates that the dawn-dusk asymmetry is caused by the open magnetopause moving to the opposite sides of the magnetosphere above and below the current sheet as the IMF B-y becomes more dominant. The HEE occurrence rates are two to three times higher on the dawn side. HEEs correlate more strongly than magnetosheath plasma with sharper transient changes in IMF direction and magnetosheath density and with quasiparallel bow shock. These correlations suggest that perturbations created at the quasiparallel bow shock can possibly cause magnetopause deformation and HEEs in the midtail, contributing to the HEE asymmetry because the quasiparallel bow shock is more often on the dawn side.