A Statistical Study of Field-Aligned Current Sheet Orientation: Dependence on Season, Hemisphere, and Solar Wind Conditions

We conducted a statistical study on the orientation of field-aligned currents (FACs) sheets in the high latitude fields of the Northern Hemisphere (NH) and Southern Hemisphere (SH) under different seasonal conditions, interplanetary magnetic field (IMF), and geomagnetic activity. We use the maximum correlation method to analyze nearly 9 years of measurements from Swarm A and C satellites. The orientation of the FAC sheets during each aurora oval crossing and the corresponding angle between the FAC sheets and the aurora boundary are derived. We find that under all conditions, the dawnside FAC sheets are clockwise at the aurora boundary, while the duskside are counterclockwise, which is similar to the flow pattern of auroral electrojet currents (AEJs) (westward on dawnside, eastward on duskside), indicating that AEJs may limit the spatial arrangement of FAC sheets. IMF By will affect the dawn-dusk asymmetry of FAC sheets arrangement, and enhanced geomagnetic activity will cause FAC sheets in both hemispheres to develop towards a more regular arrangement direction. In addition, the hemisphere and seasonal differences in FAC sheets arrangement may be related to changes in ionospheric conductivity. Our findings provide important information for the dynamic modulation of the ionospheric current system driven by external forces. In the future, the combination with SMILE satellite data will help to improve the M-I coupling model.