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Astron. Astrophys. 354, L33-L36 (2000)


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Letter to the Editor

Cyclic behaviour of sunspot activity during the Maunder minimum

I.G. Usoskin 1, K. Mursula 1 and G.A. Kovaltsov 2

1 University of Oulu, Department of Physical Sciences, 90014 University of Oulu, Finland (kalevi.mursula@oulu.fi, ilya.usoskin@oulu.fi)
2 Ioffe Phys.-Tech. Institute, 194021 St.Petersburg, Russia (gena.kovaltsov@pop.ioffe.rssi.ru)

Received 15 November 1999 / Accepted 3 January 2000

Abstract

We study the behaviour of sunspot activity in 1610-1750, i.e. just prior to, during and slightly after the Maunder minimum, using the new series of group sunspot numbers (Hoyt & Schatten 1998). We apply the delayed component technique and show that, while the transition from the normal cyclic evolution to the minimum was very abrupt, the recovery from the minimum was gradual, proceeding through a tiny but very regular cycle in 1700-1712 and a transition period with a phase catastrophe in 1712-1720. Exploiting the good coverage of the Maunder minimum by daily solar observations, we show that the sunspot ocurrence is concentrated, with a high statistical significance, to two intervals around 1658 and 1680. Together with the last sunspot maximum before the Maunder minimum in 1639/1640, and the maximum in 1705, this implies a significant, approximately 22-year periodicity in sunspot activity during the Maunder minimum.

Key words: Sun: activity – Sun: sunspots

Send offprint requests to: K. Mursula

© European Southern Observatory (ESO) 2000

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