THE POSSIBLE ASCENT OF A CLOSED MAGNETIC SYSTEM THROUGH THE PHOTOSPHERE

We present a comprehensive interpretation of the evolution of a small magnetic region observed during its entire disk passage. The vector ma gnetic field measurements from the Advanced Stokes Polarimeter, along with H alpha and magnetogram measurements from the Lockeed SOUP instru ment operating at the Swedish Solar Observatory on La Palma, and soft X-ray images from the Yohkoh satellite support the hypothesis that we have observed the passage of a nearly closed magnetic system through t he photosphere into the corona. The observations suggest that as the m agnetic flux begins to emerge into the photosphere it shows a rather s imple geometry, but it subsequently develops a small delta-sunspot con figuration with a highly sheared vector field along the polarity inver sion line running through it. At that stage, the vector field is consi stent with a concave upward magnetic topology, indicative of strong el ectric currents above the photosphere. An H alpha prominence is found above this inversion line when the delta-sunspot is fully formed. Thes e observed features and the sequence of events are interpreted in term s of a nearly closed magnetic system that rises through the photospher e into the corona as a result of magnetic buoyancy. The magnetic syste m persists in the corona well after the dark delta-sunspot has disappe ared in the photosphere. We suggest that this coronal structure is in quasi-static equilibrium with its buoyancy partially countered by the weight of the plasma trapped at the bottom of closed magnetic loops. T he plausibility of such a scenario is demonstrated by a three-dimensio nal magnetostatic model of the emergence of a closed, spheroidal magne tic system in the corona, in which the Lorentz force arising from cros s-field currents is balanced by the gravitational and pressure forces. This theoretical model carries many features in common with the obser ved morphology of our active region.