Streamer disconnection events observed with the LASCO coronagraph

Abstract

We present Large Angle Spectrometric Coronagraph (LASCO) observations of two events that suggest magnetic disconnection in coronal streamers. During the 1-2 days preceding each event, successions of narrow looptops are seen rising slowly through the 2-6 R_S field of view, forming a bright streamer stalk which continues to elongate with time. As the streamer becomes ever more constricted, it eventually severs at a heliocentric distance of ∼4 R_S. The lower part of the stalk collapses back to form a cusplike structure extending to ∼3 R_S, while the disconnected segment is observed as a kink or density enhancement that propagates outward with a speed of order 200 km s^-1. We interpret these non-CME events as transient openings and closings of magnetic flux rooted at the boundaries of coronal holes.