The Role of Reconnection at Magnetic Separators in Complex Solar Flare Ribbons

Abstract

Solar flare ribbons, manifesting as transient brightenings in the chromosphere, are believed to trace out the footpoints of magnetic field lines that are reconnecting higher in the solar atmosphere. These field lines lie in a separatrix or quasi-separatrix layer that separates domains of different magnetic connectivity and hence forms a natural location for reconnection. Solar flares are typically characterized as being circular ribbon flares, two-ribbon flares, or complex ribbon flares based on the number and shape of the ribbons. There are relatively well-developed models to explain the first two types of flares based on the location of the reconnection powering the flare. The case of complex ribbons is less well understood, but is often posited to be a result of reconnection at multiple locations. We demonstrate here that reconnection at a magnetic separator connecting two coronal null points can naturally explain the complex ribbons observed for two events, an M2.9 class flare from NOAA AR 11112 (SOL2010-10-16T19:12), and an X2.2 class flare from NOAA AR 11158 (SOL2011-02-15T01:56).