Free access article

A&A 413, 745-751 (2004)
DOI: 10.1051/0004-6361:20031533

Reconstruction of solar activity for the last millennium using Be data

I. G. Usoskin¹, K. Mursula², S. Solanki³, M. Schüssler³ and K. Alanko<sup>2

1</sup>  Sodankylä Geophysical Observatory (Oulu unit), 90014 University of Oulu, Finland
²  Department of Physical Sciences, 90014 University of Oulu, Finland
³  Max Planck Institute for Aeronomy, Katlenburg-Lindau, Germany

(Received 22 July 2003 / Accepted 26 September 2003)

Abstract
In a recent paper (Usoskin et al. 2002a), we have reconstructed the concentration of the cosmogenic ¹⁰Be isotope in ice cores from the measured sunspot numbers by using physical models for ¹⁰Be production in the Earth's atmosphere, cosmic ray transport in the heliosphere, and evolution of the Sun's open magnetic flux. Here we take the opposite route: starting from the ¹⁰Be concentration measured in ice cores from Antarctica and Greenland, we invert the models in order to reconstruct the 11-year averaged sunspot numbers since 850 AD. The inversion method is validated by comparing the reconstructed sunspot numbers with the directly observed sunspot record since 1610. The reconstructed sunspot record exhibits a prominent period of about 600 years, in agreement with earlier observations based on cosmogenic isotopes. Also, there is evidence for the century scale Gleissberg cycle and a number of shorter quasi-periodicities whose periods seem to fluctuate in the millennium time scale. This invalidates the earlier extrapolation of multi-harmonic representation of sunspot activity over extended time intervals.

Key words: sun: activity -- sun: evolution -- sun: magnetic fields -- sunspots -- stars: activity

Offprint request: I. Usoskin, ilya.usoskin@oulu.fi

SIMBAD Objects in preparation

© ESO 2004

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