Temporal variations in the magnetic network large-scale dynamics

Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées, 57 avenue d'Azereix, BP 826, 65008 Tarbes Cedex, France e-mail: meunier@bagn.obs-mip.fr

Received: 15 April 2005
Accepted: 26 July 2005

Abstract

The variation in the magnetic network large-scale dynamics is investigated using MDI magnetograms from 1996 to 2004. Cross-correlation and feature tracking techniques are used on pairs of magnetograms in order to derive the dynamics at the solar surface, including magnetic network regions. The variations for both methods are very different, the feature tracking technique leading to generally much less variable dynamics over the cycle, except for the rotation versus latitude. At cycle minimum, the increased differential rotation at high latitude combined with a more rigid rotation at low latitude is indeed more pronounced with the feature tracking. The rotation variations put a strong constraint on the origin of these variations, as some strong correlations between coefficients deduced from fits with Legendre polynomials are observed. When using the cross-correlation technique, the meridional circulation also tends to exhibit a more complex behavior compared to rotation. This study provides the temporal variations in the dependence of the dynamics on the magnetic field and feature size as well as on polarities. The dispersions in velocity for the following and leading polarities are studied over the cycle.