J. Space Weather Space Clim.
Volume 10, 2020
Topical Issue - Space climate: The past and future of solar activity
|Number of page(s)||10|
|Published online||27 August 2020|
Two-dipole model of the asymmetric Sun
Center for Space Physics, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
2 ReSoLVE Centre of Excellence, Space Climate Research Unit, University of Oulu, PO Box 3000, 90014 Oulu, Finland
* Corresponding author: email@example.com
Accepted: 28 July 2020
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.
Key words: photospheric magnetic field / north–south asymmetry / spatial power spectrum / two-dipole model
© 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 (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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