Abstract

We present a statistical investigation of the effects of interplanetary magnetic field (IMF) on hemispheric asymmetry in auroral currents. Nearly 6 years of magnetic field measurements from Swarm A and C satellites are analyzed. Bootstrap resampling is used to remove the difference in the number of samples and IMF conditions between the local seasons and the hemispheres. Currents are stronger in Northern Hemisphere (NH) than Southern Hemisphere (SH) for IMF By⁺ in NH (By⁻ in SH) in most local seasons under both signs of IMF Bz. For By⁻ in NH (By⁺ in SH), the hemispheric difference in currents is small except in local winter when currents in NH are stronger than in SH. During By⁺ and Bz⁺ in NH (By⁻ and Bz⁺ in SH), the largest hemispheric asymmetry occurs in local winter and autumn, when the NH/SH ratio of field aligned current (FAC) is 1.18±0.09 in winter and 1.17±0.09 in autumn. During (By⁺ and Bz⁻ in NH (By⁻ and Bz⁻ in SH), the largest asymmetry is observed in local autumn with NH/SH ratio of 1.16±0.07 for FAC. We also find an explicit By effect on auroral currents in a given hemisphere: on average By⁺ in NH and By⁻ in SH causes larger currents than vice versa. The explicit By effect on divergence-free current during IMF Bz⁺ is in very good agreement with the By effect on the cross polar cap potential from the Super Dual Auroral Radar Network dynamic model except at SH equinox and NH summer.