Magnetic Pinching of Hyperbolic Flux Tubes. I. Basic Estimations

Abstract

The concept of hyperbolic flux tubes (HFTs) is a generalization of the\nconcept of separator field lines for coronal magnetic fields with a trivial\nmagnetic topology. An effective mechanism of a current layer formation in HFTs\nis proposed. This mechanism is called magnetic pinching and it is caused by\nlarge-scale shearing motions applied to the photospheric feet of HFTs in a way\nas if trying to twist the HFT. It is shown that in the middle of an HFT such\nmotions produce a hyperbolic flow that causes an exponentially fast growth of\nthe current density in a thin force-free current layer. The magnetic energy\nassociated with the current layer that is built up over a few hours is\nsufficient for a large flare. Other implications of HFT pinching for solar\nflares are discussed as well.\n