Large-scale photospheric dynamics below coronal holes

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: 11 July 2005

Abstract

A large data set of MDI magnetograms is studied to analyze the global dynamics of magnetic structures from network to active regions inside and outside coronal holes. We find a weaker meridional circulation at almost all latitudes, as well as a more differential rotation of the photospheric magnetic structures below high-latitude coronal holes. Stronger asymmetries in the dynamics are observed in coronal holes at high latitude compared to outside coronal holes. The variation in the dynamics is also studied as a function of the coronal hole size as well as its variation with time and with magnetic field. The smaller velocity dispersion obtained in coronal holes when using a cross-correlation technique shows that the large-scale circulation may be inhibited inside coronal holes compared to outside. However, there is an indication of a larger diffusion of magnetic features within coronal holes than outside.