The Magnetic Topology of Solar Eruptions

We present an explanation for the well-known observation that complexity ofthe solar magnetic field is a necessary ingredient for strong activity such aslarge eruptive flares. Our model starts with the standard picture for theenergy build up -- highly-sheared, newly-emerged magnetic field near thephotospheric neutral line held down by overlying unsheared field. Previously,we proposed the key new idea that magnetic reconnection between the unshearedfield and neighboring flux systems decreases the amount of overlying field and,thereby, allows the low-lying sheared flux to ``break out'' (Antiochos, DeVoreand Klimchuk 1998, ApJ, submitted). In this paper we show that a bipolar activeregion does not have the necessary complexity for this process to occur, but adelta sunspot has the right topology for magnetic breakout. We discuss theimplications of these results for observations from SOHO and TRACE.Comment: Astrophysics Journal Latex file, 10 pages, and 2 figure