Formation of Solar Prominences by Flux Convergence

Abstract

Observations have found three main conditions that have to be fulfilled before a prominence will form. These are the presence of a magnetic arcade, a transport of flux toward the polarity inversion line under the arcade, and cancellation of magnetic flux that approaches the polarity inversion. We have set up a three-dimensional model that initially contains two bipolar regions, representing new and old regions of flux on the Sun. The regions are forced together by an imposed velocity flow on the lower boundary. As they approach one another, the magnetic field reaches a state where a thin current distribution is created above the polarity inversion line. When the current becomes strong enough, magnetic reconnection starts. In the right parameter regime it is found that the reconnected field lines are able to lift plasma several pressure scale heights against gravity. The lifted plasma forms a region with enhanced density above the current sheet, along the polarity inversion line and with a length that is longer than the length of the current sheet. Different types of field line connectivity are found that provide the force to lift mass as the reconnection proceeds.