Large-scale dynamics and polarities of magnetic structures

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: 23 November 2004
Accepted: 16 February 2005

Abstract

A large data set of MDI magnetograms is studied in order to analyse the dependence of the global dynamics of magnetic structures on their polarity. Two complementary techniques (feature tracking and correlation tracking) are used to determine the differential rotation and meridional circulation. A faster rotation of leading polarity structures is found for active areas, while a faster rotation of following polarity structures is found for weak field areas. However the latter is found only when using correlation tracking: individual small features do not seem to exhibit any difference between leading and following polarities. From correlation tracking, the mixed polarity areas (with a low activity level) do rotate as the following polarity areas. Furthermore, the latter have a more poleward motion when the correlation tracking is used.