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Astron. Astrophys. 341, L43-L46 (1999)

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Letter to the Editor

Long-term variation of sunspot latitudes

Pentti J. Pulkkinen 1, John Brooke 2,3, Jaan Pelt 4,5 and Ilkka Tuominen 5

1 Department of Physics, P.O. Box 9, University of Helsinki, FIN-00014 Helsinki, Finland
2 Manchester Computing, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
3 Department of Mathematics, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
4 Tartu Astrophysical Observatory, Töravere 1-6, Tartu, 202444, Estonia
5 Astronomy Division, University of Oulu, P.O. Box 333, FIN-90571 Oulu, Finland

Received 5 November 1998 / Accepted 23 November 1998


We consider a continuous sunspot data set ranging from 1853 to 1996. The emphasis is given to long-term activity variations and north-south asymmetries. The difference of the distance between sunspot belts and equator between the northern and southern hemispheres is considered and a systematic variation is found. The period of this variation is about 8.4 sunspot cycles or about 90 years, and the amplitude is 1.3 degrees. This phenomenon could be explained by oscillation of a quadrupolar component of solar mixed parity mode magnetic field.

Key words: Sun: activity – Sun: magnetic fields – Sun: photosphere – Sun: sunspots

Send offprint requests to: Pentti Pulkkinen (pentti.pulkkinen@helsinki.fi)

© European Southern Observatory (ESO) 1999

Online publication: December 4, 1998