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Issue
A&A
Volume 405, Number 3, July III 2003
Page(s) 1121 - 1128
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20030748


A&A 405, 1121-1128 (2003)
DOI: 10.1051/0004-6361:20030748

Active longitudes in sunspot activity: Century scale persistence

S. V. Berdyugina1, 2 and I. G. Usoskin3

1  Institut für Astronomie, ETHZ, 8092 Zürich, Switzerland
2  Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
    e-mail: sveta.berdyugina@oulu.fi
3  Sodankylä Geophysical Observatory (Oulu unit), 90014 University of Oulu, Finland
    e-mail: ilya.usoskin@oulu.fi

(Received 6 November 2002 / Accepted 12 May 2003)

Abstract
A novel analysis of sunspot group data for the past 120 years reveals that sunspots in both northern and southern hemispheres are formed preferably in two persistent active longitudes separated by 180°. In the Carrington reference frame, the active longitudes continuously migrate in phase with respect to the Carrington meridian with a variable rate. They remain however a quasi-rigid structure. We find that the migration of the active longitudes is determined by changes of the mean latitude of sunspots and the differential rotation. The differential rotation rate calculated from the migration is in agreement with SOHO/MDI measurements. The two active longitude periodically alternate being the dominant region, similar to the "flip-flop" phenomenon known in starspot activity. The period of the oscillations is 3.8 and 3.65 years in the north and south, respectively. The difference between the periods is significant and can be related to the known north-south asymmetry in the solar magnetic activity. Our results provide new observational constraints for current solar dynamo models and strengthen the solar paradigm for magnetic activity on cool stars.


Key words: Sun: activity -- Sun: magnetic fields -- sunspots -- stars: activity

Offprint request: S. V. Berdyugina, sveta@astro.phys.ethz.ch




© ESO 2003