University of Oulu

Koskela, J., Virtanen, I., Mursula, K. (2019) Revisiting the coronal current sheet model: Parameter range analysis and comparison with the potential field model. Astronomy and astrophysics , 631, A17. doi:10.1051/0004-6361/201935967

Revisiting the coronal current sheet model: parameter range analysis and comparison with the potential field model : parameter range analysis and comparison with the potential field model

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Author: Koskela, Jennimari1; Virtanen, Ilpo1; Mursula, Kalevi1
Organizations: 1ReSoLVE Centre of Excellence, Space Climate Research Unit, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 3.1 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2019122049112
Language: English
Published: EDP Sciences, 2019
Publish Date: 2019-12-20
Description:

Abstract

Aims:. We study the properties of the coronal magnetic field according to the current sheet source surface (CSSS) model in 1976–2017 for all physically reasonable values of the three model parameters (cusp surface radius Rcs, source surface radius Rss, and current parameter a), and compare the CSSS field with the potential field source surface (PFSS) model field.

Methods: We used the synoptic maps of the photospheric magnetic field from the Wilcox Solar Observatory (WSO), National Solar Observatory/Kitt Peak (NSO/KP), and the NSO Synoptic Optical Long-term Investigations of the Sun Vector Spectromagnetograph (SOLIS/VSM) in order to calculate the coronal magnetic field according to the CSSS and PFSS models. We calculated the coronal field strength, its latitudinal variation and neutral line location, as well as its polarity match with the heliospheric magnetic field.

Results: The CSSS model can correct the erroneous latitudinal variation of the PFSS model if the source surface is sufficiently far out with respect to the cusp surface (Rss ≥ 3 ⋅ Rcs). The topology of the neutral line only slightly depends on source surface radius or current parameter, but excludes very low values of the cusp surface (Rcs ≤ 1.5). A comparison of the polarities gives an optimum cusp surface radius that varies in time between 2 and 5; a stronger current yields a larger optimum Rcs. Interestingly, the optimum polarity match percentages and optimum radii vary very similarly in the two models over the four solar cycles we studied.

Conclusions: The CSSS model can produce a stronger total coronal flux than the PFSS model and correct its latitudinal variation. However, the topology of the CSSS model is rather independent of horizontal currents and remains very similar to that of the PFSS model. Therefore, the CSSS model cannot improve the match of field polarities between corona and heliosphere.

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Series: Astronomy and astrophysics
ISSN: 0004-6361
ISSN-E: 1432-0746
ISSN-L: 0004-6361
Volume: 631
Article number: A17
DOI: 10.1051/0004-6361/201935967
OADOI: https://oadoi.org/10.1051/0004-6361/201935967
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Subjects:
Funding: We 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: © ESO, 2019. Published in this repository with the kind permission of the publisher.