Effect of Interplanetary Magnetic Field on Hemispheric Asymmetry in Ionospheric Horizontal and Field‐Aligned Currents During Different Seasons

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...

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Bibliographic Details
Published in:Journal of geophysical research. Space physics 2021-10, Vol.126 (10), p.n/a
Main Authors: Workayehu, A. B., Vanhamäki, H., Aikio, A. T., Shepherd, S. G.
Format: Article
Language:English
Subjects:
Asymmetry
Autumn
Dynamic models
Field aligned currents
Interplanetary magnetic field
Magnetic fields
Northern Hemisphere
Polar caps
Radar
Radar networks
Resampling
Seasons
Southern Hemisphere
Statistical methods
Winter
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Summary: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. Key Points Hemispheric asymmetry in auroral currents is larger for interplanetary magnetic field (IMF) By+ in the Northern Hemisphere (NH) (By− in the Southern Hemisphere [SH]) than vice versa during both signs of IMF Bz Strongest asymmetry occurs in local winter and autumn for By+ in the NH (By− in the SH) and IMF Bz+ with NH/SH field aligned current ratio of about 1.18 IMF By+ in the NH and By− in the SH causes larger auroral currents than vice versa. Effect is stronger for IMF Bz+ than for IMF Bz−
ISSN:2169-9380
2169-9402
DOI:10.1029/2021JA029475