Letter to the Editor

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

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

Corresponding author: R. Knaack, rknaack@astro.phys.ethz.ch

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 ± , 1.79 ± and 3.6 ± 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 ± (twice the magnetic cycle) and were detected in the sunspot asymmetry.