How to form a dip in a magnetic field before the formation of a solar prominence

Abstract

Magnetic fields with downward curvature are not favourable for prominence formation since the presence of a small quantity of dense material at the summit of a low-beta arcade cannot deform sufficiently the magnetic field lines to remain there in a stable manner. Thus a dip at the field line summit is needed before a prominence can form. We investigate different ways of forming such an upward curvature. Results with a twisted flux tube or a sheared arcade are reviewed, and a third possibility, namely a quadrupolar region is proposed.