Free access article

A&A 475, L33-L36 (2007)
DOI: 10.1051/0004-6361:20078672

Letter

Scale-resolved phase coherence analysis of hemispheric sunspot activity: a new look at the north-south asymmetry

R. Donner^{1, 2} and M. Thiel<sup>3, 2

1</sup>  Institute for Transport and Economics, Dresden University of Technology, Andreas-Schubert-Str. 23, 01062 Dresden, Germany
    e-mail: donner@vwi.tu-dresden.de
²  Nonlinear Dynamics Group, Department of Physics, University of Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany
³  Department of Physics, University of Aberdeen, Aberdeen AB24 3UE, Scotland, UK

(Received 14 September 2007 / Accepted 11 October 2007)

Abstract
Aims.The sunspot activity on both solar hemispheres is known to show time intervals of different phase relationships. In this letter, we introduce an advanced statistical framework that allows an appropriate analysis of these relationships.
Methods.We combine wavelet analysis with statistical measures of phase coherence to obtain well-defined phase differences in dependence on the selected oscillation period.
Results.Our approach characterises the temporally varying phase difference of the hemispheric sunspot activity over the past 130 years, which is a major contribution to the north-south asymmetry. Coherent phase variables are found to exist for a frequency band with periodicities around the dominating 11-year cycle. We observe significant continuous long-term variability of interhemispheric phase shifts, which is not reproduced by solar activity records from previous centuries.

Key words: Sun: sunspots -- Sun: activity

© ESO 2007

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