Periodic oscillations in the north–south asymmetry of the solar magnetic field

Free access article

Issue		A&A Volume 418, Number 1, April IV 2004


Page(s)		L17 - L20
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20040107

A&A 418, L17-L20 (2004)
DOI: 10.1051/0004-6361:20040107

Letter

Periodic oscillations in the north-south asymmetry of the solar magnetic field

R. Knaack¹, J. O. Stenflo^{1, 2} and S. V. Berdyugina^{1, 3}

¹ Institute of Astronomy, ETH-Zentrum, 8092 Zürich, Switzerland
e-mail: [rknaack;stenflo;sveta]@astro.phys.ethz.ch
² Faculty of Mathematics and Science, University of Zurich, 8057 Zürich, Switzerland
³ Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland

(Received 10 February 2004 / Accepted 4 March 2004)

Abstract
We report on significant periodic variations of the magnetic activity between the north and south hemisphere of the Sun. For this purpose, we have investigated the north-south asymmetry of two solar data sets, namely the Kitt Peak synoptic Carrington rotation maps of the photospheric magnetic field (1975-2003) and monthly averaged sunspot areas (1874-2003). Using Fourier and wavelet analysis, we have found a regular pattern of pronounced oscillations with periods of 1.50 $\pm$ $0.04~{\rm yr}$ , 1.79 $\pm$ $0.06~{\rm yr}$ and 3.6 $\pm$ $0.3~{\rm yr}$ in the magnetic flux asymmetry. The former two periods are related to a process which leads to a gradual shift in the excess magnetic flux from north to south or vice versa. Additional periods of 43.4 $\pm$ $7.1~{\rm yr}$ (twice the magnetic cycle) and $320{-}329~{\rm days}$ were detected in the sunspot asymmetry.

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

Offprint request: R. Knaack, rknaack@astro.phys.ethz.ch

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