This article has an erratum: [erratum]

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

Active longitudes in sunspot activity: Century scale persistence

S. V. Berdyugina^{1, 2} and I. G. Usoskin<sup>3

1</sup>  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

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

• If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
• You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
• You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.