University of Oulu

Virtanen, I. O. I., Pevtsov, A. A., Virtanen, I. I., & Mursula, K. (2021). Reconstructing solar magnetic fields from historical observations. In Astronomy & Astrophysics (Vol. 652, p. A79). EDP Sciences.

Reconstructing solar magnetic fields from historical observations : VII. Far-side activity in surface flux transport simulations

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Author: Virtanen, I. O. I.1; Pevtsov, A. A.2; Virtanen, I. I.1;
Organizations: 1Space physics and astronomy research unit, University of Oulu, PO Box 3000, 90014 Oulu, Finland
2National Solar Observatory, Boulder, CO 80303, USA
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 7.6 MB)
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Language: English
Published: EDP Sciences, 2021
Publish Date: 2021-10-21


Context: The evolution of the photospheric magnetic field can be simulated with surface flux transport (SFT) simulations, which allow for the study of the evolution of the entire field, including polar fields, solely using observations of the active regions. However, because only one side of the Sun is visible at a time, active regions that emerge and decay on the far-side are not observed and not included in the simulations. As a result, some flux is missed.

Aims: We construct additional active regions and apply them to the far-side of the Sun in an SFT simulation to assess the possible effects and the magnitude of error that the missing far-side flux causes. We estimate how taking the missing far-side flux into account affects long-term SFT simulations.

Methods: We identified active regions from synoptic maps of the photospheric magnetic field between 1975 and 2019. We divided them into solar cycle wings and determined their lifetimes. Using the properties of observed active regions with sufficiently short lifetimes, we constructed additional active regions and inserted them into an SFT simulation.

Results: We find that adding active regions with short lifetimes to the far-side of the Sun results in significantly stronger polar fields in minimum times and slightly delayed polarity reversals. These results partly remedy the earlier results, which show overly weak polar fields and polarity reversals that are slightly too early when far-side emergence is not taken into account. The far-side active regions do not significantly affect poleward flux surges, which are mostly caused by larger long-living active regions. The far-side emergence leads to a weak continuous flow of flux, which affects polar fields over long periods of time.

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Series: Astronomy and astrophysics
ISSN: 0004-6361
ISSN-E: 1432-0746
ISSN-L: 0004-6361
Volume: 652
Article number: A79
DOI: 10.1051/0004-6361/202140656
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Copyright information: © ESO 2021.