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Astron. Astrophys. 332, 748-754 (1998)

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Velocity structures from sunspot statistics in cycles 10 to 22

I. Rotational velocity

Pentti Pulkkinen 1, 2 and Ilkka Tuominen 2

1 Department of Physics, P.O. Box 9, SF-00014, University of Helsinki, Finland
2 Astronomy Division, University of Oulu, P.O. Box 333, SF-90571 Oulu, Finland

Received 11 July 1997 / Accepted 11 December 1997


Data from the whole era of modern sunspot observations (1853-1996) from four different sources is considered. We find that rotation is continuously changing, not only in the course of a cycle but also in a longer time period. We also find strong fluctuations in the equatorial rotation in the course of a sunspot cycle which can be connected with the observed north/south asymmetry of rotation. The importance of age dependence on rotation is emphasized, both for non-recurrent and recurrent sunspots as the slowing down of rotation along with the age is confirmed.

Key words: Sun: activity – Sun: photosphere – Sun: rotation – sunspots

Send offprint requests to: Pentti Pulkkinen

© European Southern Observatory (ESO) 1998

Online publication: March 23, 1998