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 the footpoints of magnetic field lines reconnecting higher in the solar atmosphere. These field lines lie within separatrix or quasi-separatrix layers that separate domains of different magnetic connectivity and hence form natural locations for reconnection. Solar flares are typically characterized as 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 for the first two types of flares based on the location of the reconnection powering the flare. Complex ribbons are less well understood, but are often posited as the result of reconnection at multiple locations. Here, we demonstrate that reconnection at a magnetic separator connecting two coronal null points can naturally explain the complex ribbons observed in 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).