DISRUPTION OF HELMET STREAMERS BY CURRENT EMERGENCE

We have investigated the dynamic response of a coronal helmet streamer to the emergence from below of a current with its magnetic field in a direction opposite to the overlying streamer field. Once the emerging current moves into the closed region of the streamer, a current sheet forms between the emerging field and the streamer field, because the preexisting held and the newly emerging field have opposite polarities , Thus magnetic reconnection will occur at the flanks of the emerged s tructure where the current density is maximum. If the emerging current is large enough, the energy contained in the current and the reconnec tion will promptly disrupt the streamer. If the emerging current is sm all, the streamer will experience a stage of slow evolution. In this s tage, slow magnetic reconnection occurring at the hanks of the emerged structure leads to the degeneration of the emerged current to a neutr al point. Above this point, a new magnetic bubble will form. The resul ting configuration resembles an inverse-polarity prominence. Depending on the initial input energy of the current, the resulting structure w ill either remain in situ, forming a quasi-static structure, or move u pward, forming a coronal transient similar to coronal jets. The numeri cal method used in this paper can be used to construct helmet streamer s containing a detached magnetic structure in their closed field regio n. The quasi-static solution may serve as a preevent corona for studyi ng coronal mass ejection initiation.