Zero points of the magnetic field in the solar atmosphere

Abstract

Examples of saddle structures observed in images of the Sun in Hα, soft X-ray (YOHKOH SXT), and ultraviolet (SOHO EIT) emission are presented. Since the plasma distribution is controlled by the magnetic field, the saddles testify to the presence of hyperbolic singularities in the magnetic field. Such singularities play an important role in the theory of flare energy release. It is usually supposed that conditions for the development of current sheets arise in them, leading to magnetic reconnection, which transforms magnetic energy into thermal and kinetic energy. The observed saddle structures can correspond either to two-dimensional or three-dimensional magnetic-field singularities, depending on the geometry, projection, symmetry, and so on. In nearly all cases, the central parts of the saddles remain dark, and do not exhibit additional energy release.