Sheared coronal arcades: An evaluation of recent studies

Abstract

We show that the family of magnetic force-free equilibria obtained by Low using the generating function method is really a sequence of Gold-Hoyle flux tubes. This sequence is stable under a wide range of solar conditions since each member, specified by the shear parameter μ, is anchored to the photosphere along an axial slice. We go on to demonstrate that recent magnetic relaxation simulations by Klimchuk and Sturrock are fundamentally incapable of representing the unconnected helical field lines inherent in the high-shear (μ > 1) Low solutions. Nonetheless, we believe that the numerical simulations are more likely to describe the equilibria of highly sheared arcades since they involve no change in topology with increasing shear. This view is reinforced by magnetic energy calculations which confirm that the Gold-Hoyle solutions are more energetic for μ > 1 than the numerical equilibria of Klimchuk and Sturrock.