University of Oulu

Holappa, L., Robinson, R. M., Pulkkinen, A., Asikainen, T., & Mursula, K. (2021). Explicit IMF By-dependence in geomagnetic activity: Quantifying ionospheric electrodynamics. Journal of Geophysical Research: Space Physics, 126, e2021JA029202.

Explicit IMF By-dependence in geomagnetic activity : quantifying ionospheric electrodynamics

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Author: Holappa, L.1,2,3; Robinson, R. M.2,3; Pulkkinen, A.3;
Organizations: 1Space Climate Research Group, Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
2Catholic University of America, Washington, DC, USA
3NASA Goddard Space Flight Center, Greenbelt, MD, USA
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.2 MB)
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Language: English
Published: American Geophysical Union, 2021
Publish Date: 2021-06-30


Geomagnetic activity is mainly driven by the southward (Bz) component of the interplanetary magnetic field (IMF), which dominates all solar wind coupling functions. Coupling functions also depend on the absolute value of the dawn-dusk (By) component of the IMF, but not on its sign. However, recent studies have shown that for a fixed level of solar wind driving, auroral electrojets in the Northern Hemisphere (NH) are stronger for By > 0 than for By < 0 during NH winter. In NH summer, the dependence on the By sign is reversed. While this By sign dependence, also called the explicit By-dependence, is very strong in the winter hemisphere, it is weak in the summer hemisphere. Moreover, the explicit By-dependence is much stronger in the westward electrojet than in the eastward electrojet. In this study, we study how the explicit IMF By-dependence is coupled with large-scale field-aligned currents (FACs) by using FAC measurements from the Active Magnetosphere and Planetary Electrodynamics Response Experiment and an empirical ionospheric conductance model. We model the complete ionospheric electrodynamics by solving the current continuity equation, and show that during periods of elevated solar wind driving (Bz < 0), the IMF By component modulates Regions 1 and 2 FACs in the dawn sector of the winter hemisphere. This leads to an explicit By-dependence in ionospheric conductance and the westward electrojet. We also show that the By-dependence of FACs and conductance is weak in the dusk sector, which explains the earlier observation of the weak By-dependence of the eastward electrojet.

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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: 4
Article number: e2021JA029202
DOI: 10.1029/2021JA029202
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: The authors acknowledge the financial support by the Academy of Finland to the Postdoctoral Researcher project of L. Holappa (No. 322459) and to the PROSPECT project (No. 321440). This study was supported at Goddard Space Flight Center by NASA Cooperative Agreement NNG11PL10A, the Community Coordinated Modeling Center, and the TIMED/GUVI Project (NASA Grant NNX14AK74G). We thank the AMPERE team and the AMPERE Science Center for providing the Iridium-derived data products. AMPERE data used in this paper are publically available through the AMPERE web site: The solar wind data (solar wind speed and different components of IMF) were downloaded from the OMNI2 database ( ​
Academy of Finland Grant Number: 322459
Detailed Information: 322459 (Academy of Finland Funding decision)
321440 (Academy of Finland Funding decision)
Copyright information: © 2021. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.