EDP Sciences
Free Access
Volume 383, Number 2, February IV 2002
Page(s) 706 - 712
Section The Sun
DOI https://doi.org/10.1051/0004-6361:20011790
Published online 15 February 2002

A&A 383, 706-712 (2002)
DOI: 10.1051/0004-6361:20011790

Secular variation of the Sun's magnetic flux

S. K. Solanki1, M. Schüssler1 and M. Fligge2

1  Max-Planck-Institut für Aeronomie, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany
    e-mail: solanki@linmpi.mpg.de, schuessler@linmpi.mpg.de
2  Institut für Astronomie, ETH-Zentrum, 8092 Zürich, Switzerland

(Received 18 September 2001 / Accepted 7 December 2001 )

We present an extension of the model of Solanki et al. (2000) that allows us to reconstruct the time evolution of both the total and the open magnetic flux at the solar surface since 1700. The flux emerging in large active regions is determined using the sunspot number as a proxy, while the flux emergence in small ephemeral regions is described by an extended cycle whose amplitude and length are related to the corresponding sunspot cycle. Both types of regions contribute to the open flux, which is the source of the heliospheric field. The overlap of the activity cycles of ephemeral regions leads to a secular variation of the total cycle-related magnetic flux (active region flux + ephemeral region flux + open flux). The model results indicate that the total surface flux has doubled in the first half of the last century. The evolution of the open flux is in good agreement with the reconstruction by Lockwood et al. (1999).

Key words: Sun: magnetic fields -- Sun: activity -- solar-terrestrial relations

© ESO 2002

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