Solar and stellar coronae

Abstract

A review of the observational facts of the X-ray corona of the sun suggests that the dissipation of waves plays at most a minor role in heating the corona. On the other hand, the random continuous shuffling and mixing of the footpoints of the bipolar magnetic fields, in which the X-ray corona resides, causes the spontaneous appearance of current sheets. Current sheets are highly dissipative, with a tendency to transient bursts of magnetic reconnection. Detailed observations show that the X-ray corona is made up of large numbers of small intense impulsive events of the same magnitude as expected from the bursts of reconnection. It appears, then, that it is the spontaneous current sheets that are the direct cause of the X-ray corona, driven by the continuous motions of the footpoints of the field in the photospheric convection.