Evolution and Flare Activity of δ-Sunspots in Cycle 23

Abstract

The emergence and magnetic evolution of solar active regions (ARs) of βγδ-type, which are known to be highly flare-productive, were studied with SOHO/MDI data in Cycle 23. We selected 31 ARs that can be observed from their birth phase as unbiased samples for our study. From the analysis of the magnetic topology (twist and writhe), we obtained the following results: i) Emerging βγδ ARs can be classified into three topological types as quasi-β, writhed, and top-to-top. ii) Of these, the writhed and top-to-top types tend to show high flare activity. iii) As the signs of twist and writhe agree with each other in most cases of the writhed type (12 cases out of 13), we propose a magnetic model in which the emerging flux regions in a βγδ AR are not separated, but are united as a single structure below the solar surface. iv) Almost all the writhed-type ARs have downward knotted structures in the middle part of the magnetic flux tube. This is probably the essential property of βγδ ARs. v) The flare activity of βγδ ARs is highly correlated not only with the sunspot area, but also with the magnetic complexity. vi) We suggest that there is a possible scaling-law between the flare index and the maximum umbral area