University of Oulu

Workayehu, A. B., Vanhamäki, H., Aikio, A. T., & Shepherd, S. G. (2021). Effect of interplanetary magnetic field on hemispheric asymmetry in ionospheric horizontal and field-aligned currents during different seasons. Journal of Geophysical Research: Space Physics, 126, e2021JA029475.

Effect of interplanetary magnetic field on hemispheric asymmetry in ionospheric horizontal and field-aligned currents during different seasons

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Author: Workayehu, A. B.1; Vanhamäki, H.1; Aikio, A. T.1;
Organizations: 1Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
2Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 4.9 MB)
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Language: English
Published: American Geophysical Union, 2021
Publish Date: 2022-03-24


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.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 126
Issue: 10
Article number: e2021JA029475
DOI: 10.1029/2021JA029475
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work was supported by the Academy of Finland (project 314664) and support for S. G. Shepherd provided by National Science Foundation (grant AGS-1934997).
Academy of Finland Grant Number: 314664
Detailed Information: 314664 (Academy of Finland Funding decision)
Copyright information: © 2021. American Geophysical Union.