Effect of interplanetary magnetic field on hemispheric asymmetry in
ionospheric horizontal and field-aligned currents during different
seasons
Abstract
We present a statistical investigation of the effects of interplanetary
magnetic field (IMF) on hemispheric asymmetry in auroral currents.
Nearly six 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 B$y^+$ in NH
(B$y^-$ in SH) in most local seasons under both signs of IMF
B$z$. For B$y^-$ in NH (B$y^+$ in SH), the hemispheric
difference in currents is small except in local winter when currents in
NH are stronger than in SH. During B$y^+$ and B$z^+$ in NH
(B$y^-$ and B$z^+$ 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$\pm$0.09 in winter and
1.17$\pm$0.09 in autumn. During B$y^+$ and
B$z^-$ in NH (B$y^-$ and B$z^-$ in SH), the largest
asymmetry is observed in local autumn with NH/SH ratio of
1.16$\pm$0.07 for FAC. We also find an explicit B$y$
effect on auroral currents in a given hemisphere: on average B$y^+$
in NH and B$y^-$ in SH causes larger currents than vice versa. The
explicit B$y$ effect on divergence-free (DF) current during IMF
B$z^+$ is in very good agreement with the B$y$ effect on the
cross polar cap potential (CPCP) from the Super Dual Auroral Radar
Network (SuperDARN) dynamic model except at SH equinox and NH summer.