University of Oulu

Pedersen, M. N., Vanhamäki, H., Aikio, A. T., Käki, S., Workayehu, A. B., Waters, C. L., & Gjerloev, J. W. (2021). Field-aligned and ionospheric currents by AMPERE and SuperMAG during HSS/SIR-driven storms. Journal of Geophysical Research: Space Physics, 126, e2021JA029437.

Field-aligned and ionospheric currents by AMPERE and SuperMAG during HSS/SIR-driven storms

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Author: Pedersen, M. N.1; Vanhamäki, H.1; Aikio, A. T.1;
Organizations: 1Space physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
2Finnish Meteorological Institute, Helsinki, Finland
3Division of Particle Physics and Astrophysics, University of Helsinki, Helsinki, Finland
4School of Mathematical and Physical Sciences, University of Newcastle, Callaghan, NSW, Australia
5The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
6Faculty for physics and technology, University of Bergen, Bergen, Norway
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 3.6 MB)
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Language: English
Published: American Geophysical Union, 2021
Publish Date: 2022-04-05


This study considers 28 geomagnetic storms with Dst ≤ −50 nT driven by high-speed streams (HSSs) and associated stream interaction regions (SIRs) during 2010–2017. Their impact on ionospheric horizontal and field-aligned currents (FACs) have been investigated using superposed epoch analysis of SuperMAG and AMPERE data, respectively. The zero epoch (t₀) was set to the onset of the storm main phase. Storms begin in the SIR with enhanced solar wind density and compressed southward oriented magnetic field. The integrated FAC and equivalent currents maximize 40 and 58 min after t₀, respectively, followed by a small peak in the middle of the main phase (t₀ + 4 hr), and a slightly larger peak just before the Dst minimum (t₀ + 5.3 hr). The currents are strongly driven by the solar wind, and the correlation between the Akasofu ε and integrated FAC is 0.90. The number of substorm onsets maximizes near t₀. The storms were also separated into two groups based on the solar wind dynamic pressure pdyn in the vicinity of the SIR. High pdyn storms reach solar wind velocity maxima earlier and have shorter lead times from the HSS arrival to storm onset compared with low pdyn events. The high pdyn events also have sudden storm commencements, stronger solar wind driving and ionospheric response at t₀, and are primarily responsible for the first peak in the currents after t₀. After t₀ + 2 days, the currents and number of substorm onsets become higher for low compared with high pdyn events, which may be related to higher solar wind speed.

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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: 11
Article number: e2021JA029437
DOI: 10.1029/2021JA029437
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 314670.
Academy of Finland Grant Number: 314664
Detailed Information: 314664 (Academy of Finland Funding decision)
314670 (Academy of Finland Funding decision)
Copyright information: © 2021. American Geophysical Union. All Rights Reserved.