Magnetic Pinching of Hyperbolic Flux Tubes: I. Basic Estimations
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The concept of hyperbolic flux tubes (HFTs) is a generalization of the concept of separator field lines for coronal magnetic fields with a trivial magnetic topology. An effective mechanism of a current layer formation in HFTs is proposed. This mechanism is called magnetic pinching and it is caused by large-scale shearing motions applied to the photospheric feet of HFTs in a way as if trying to twist the HFT. It is shown that in the middle of an HFT such motions produce a hyperbolic flow that causes an exponentially fast growth of the current density in a thin force-free current layer. The magnetic energy associated with the current layer that is built up over a few hours is sufficient for a large flare. Other implications of HFT pinching for solar flares are discussed as well.
31 pages, 12 figures, accepted to Astrophysical Journal, added typos in Eq. (A9) and new comments to Sections 2 and 7, references updated
31 pages, 12 figures, accepted to Astrophysical Journal, added typos in Eq. (A9) and new comments to Sections 2 and 7, references updated