The Making of Delta Sunspots

Abstract We explore what fraction of delta sunspots with a sharp polarity inversion line (PIL) in photospheric magnetograms are produced by a writhe kink in an emerging twisted flux rope. Using simultaneous full-disk magnetograms and continuum images from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory, we identified 28 random sharp-PIL delta sunspots that form well on the disk. Only one of these formed from a single newly emerged bipolar magnetic region (BMR) and is therefore a candidate for being produced by a single emerging writhe-kinked flux rope. This outcome indicates that few, if any, sharp-PIL delta sunspots are produced by a single emerging writhe-kinked flux rope; this is the main new finding of this paper. The remaining 27 are produced by the merging of two or more emerging or emerged BMRs. We refer to delta-sunspot genesis from a single BMR as Type I genesis. Among the other 27 delta sunspots, we identify three additional genesis types: Type II, Type III, and Type IV. For each of the four genesis types we present an observed example and schematic drawings depicting our proposed formation scenario(s). The core idea of these scenarios is that delta sunspots form when opposite-polarity magnetic flux is packed together by advection into a convective downflow.