A Model of Solar X-ray Bright Points and Ephemeral Active Regions

Abstract

Solar ephemeral active regions may provide a larger amount of emerging magnetic flux than the active regions themselves, and the origin and disposal of this flux pose problems. The related X-ray bright points are a major feature of coronal dynamics, and the two phenomena may entail a revision of our ideas of the activity cycle. A new large-scale subsurface magnetic field system has been suggested, but it is shown that such a system is neither plausible nor necessary. The emerging magnetic bipoles merely represent loops in pre-existing vertical flux tubes which are parts of active regions or the remnants of active regions. These loops result from the kink (or helical) instability in a twisted flux tube. Their observed properties are explained in terms of the flux-rope theory of solar fields. The model is extended to some dynamical effects in emerging loops. Further observations of ephemeral active regions may provide important tests between the traditional and flux-rope theories of solar magnetic fields.