University of Oulu

Zieger B & Mursula K. 2020. Two-dipole model of the asymmetric Sun. J. Space Weather Space Clim.10, 40.

Two-dipole model of the asymmetric Sun

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Author: Zieger, Bertalan1; Mursula, Kalevi2
Organizations: 1Center for Space Physics, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
2ReSoLVE Centre of Excellence, Space Climate Research Unit, University of Oulu, PO Box 3000, 90014 Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.5 MB)
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Language: English
Published: EDP Sciences, 2020
Publish Date: 2020-11-13


The large-scale photospheric magnetic field is commonly thought to be mainly dipolar during sunspot minima, when magnetic fields of opposite polarity cover the solar poles. However, recent studies show that the octupole harmonics contribute comparably to the spatial power of the photospheric field at these times. Also, the even harmonics are non-zero, indicating that the Sun is hemispherically asymmetric with systematically stronger fields in the south during solar minima. We present here an analytical model of two eccentric axial dipoles of different strength, which is physically motivated by the dipole moments produced by decaying active regions. With only four parameters, this model closely reproduces the observed large-scale photospheric field and all significant coefficients of its spherical harmonics expansion, including the even harmonics responsible for the solar hemispheric asymmetry. This two-dipole model of the photospheric magnetic field also explains the southward shift of the heliospheric current sheet observed during recent solar minima.

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Series: Journal of space weather and space climate
ISSN: 2115-7251
ISSN-E: 2115-7251
ISSN-L: 2115-7251
Volume: 10
Article number: 40
DOI: 10.1051/swsc/2020041
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 ReSoLVE Centre of Excellence (Project No. 307411).
Academy of Finland Grant Number: 307411
Detailed Information: 307411 (Academy of Finland Funding decision)
Copyright information: © B. Zieger & K. Mursula, Published by EDP Sciences 2020. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.