Migration and Extension of Solar Active Longitudinal Zones
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Migration and Extension of Solar Active Longitudinal Zones N. Gyenge · T. Baranyi · A. Ludmány
Received: 30 August 2012 / Accepted: 24 September 2013 / Published online: 12 November 2013 © Springer Science+Business Media Dordrecht 2013
Abstract Solar active longitudes show a characteristic migration pattern in the Carrington coordinate system if they can be identified at all. By following this migration, the longitudinal activity distribution around the center of the band can be determined. The half-width of the distribution is found to be varying in Cycles 21 – 23, and in some time intervals it was as narrow as 20 – 30 degrees. It was more extended around a maximum but it was also narrow when the activity jumped to the opposite longitude. Flux emergence exhibited a quasi-periodic variation within the active zone with a period of about 1.3 years. The path of the active-longitude migration does not support the view that it might be associated with the 11-year solar cycle. These results were obtained for a limited time interval of a few solar cycles and, bearing in mind uncertainties of the migration-path definition, are only indicative. For the major fraction of the dataset no systematic active longitudes were found. Sporadic migration of active longitudes was identified only for Cycles 21 – 22 in the northern hemisphere and Cycle 23 in the southern hemisphere. Keywords Sunspots · Solar activity
1. Introduction The spatial distribution of active-region emergence has been investigated since the creation of the Carrington coordinate system. The equatorward latitudinal migration of sunspot
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N. Gyenge ( ) · T. Baranyi · A. Ludmány Heliophysical Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O. Box 30, 4010 Debrecen, Hungary e-mail: [email protected] T. Baranyi e-mail: [email protected] A. Ludmány e-mail: [email protected]
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group emergence was first observed by Carrington in 1859, a phenomenon later named after Spörer, and Carrington was also the first to observe active-region emergences at the same longitudes (Carrington, 1863). Since then numerous works have been devoted to the longitudinal grouping of activity. Different terminology has been used but the aim was always to reveal whether the emergence is equally probable at any longitude, or if not, what the extent of deviation from the axial symmetry is and where the locations of higher-than-average activity are. This is a much more difficult challenge than the study of latitudinal patterns because one cannot assume that the location of enhanced activity is bound to the Carrington system. The diversity of results obtained can partly be explained by the differences of the methods applied, pre-assumptions, input data, and time intervals. Several attempts have been made to identify the rotation rate of the frame to which the sources of enhanced activity can be
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