University of Oulu

Holappa, L., Gopalswamy, N., & Mursula, K. (2019). Explicit IMF By‐effect maximizes at subauroral latitudes (dedicated to the memory of Eigil Friis‐Christensen). Journal of Geophysical Research: Space Physics, 124, 2854– 2863.

Explicit IMF By‐effect maximizes at subauroral latitudes (dedicated to the memory of Eigil Friis‐Christensen)

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Author: Holappa, L.1,2,3; Gopalswamy, N.2; Mursula, K.1
Organizations: 1ReSoLVE Centre of Excellence, Space Physics Research Unit, University of Oulu, Oulu, Finland
2NASA Goddard Space Flight Center, Greenbelt, MD, USA
3Department of Physics, Catholic University of America, Washington, DC, USA
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.6 MB)
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Language: English
Published: American Geophysical Union, 2019
Publish Date: 2019-10-12


The most important parameter in the coupling between solar wind and geomagnetic activity is the Bz‐component of the interplanetary magnetic field (IMF). However, recent studies have shown that IMF By is an additional, independent driver of geomagnetic activity. We use here local geomagnetic indices from a large network of magnetic stations to study how IMF By affects geomagnetic activity at different latitudes for all solar wind and, separately, during coronal mass ejections. We show that geomagnetic activity, for all solar wind, is 20% stronger for By > 0 than for By < 0 at subauroral latitudes of about 60° corrected geomagnetic latitude. During coronal mass ejections, the By‐effect is larger, about 40%, at slightly lower latitudes of about 57° (corrected geomagnetic) latitude. These results highlight the importance of the IMF By‐component for space weather at different latitudes and must be taken into account in space weather modeling.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 124
Issue: 4
Pages: 2854 - 2863
DOI: 10.1029/2018JA026285
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: Academy of Finland (Suomen Akatemia). Grant Number: 272157.
Academy of Finland Grant Number: 272157
Detailed Information: 272157 (Academy of Finland Funding decision)
Copyright information: © 2019. American Geophysical Union. All Rights Reserved.