Evolution and Flare Activity of Delta-Sunspots in Cycle 23

TL;DR

This study investigates the magnetic evolution and flare activity of beta-gamma-delta solar active regions in Cycle 23, classifying their topologies and linking magnetic complexity to flare productivity.

Contribution

It introduces a classification of emerging beta-gamma-delta ARs based on magnetic topology and proposes a magnetic model uniting flux regions, highlighting properties linked to flare activity.

Findings

Writhed and top-to-top types tend to be highly flare-productive.

Most writhed types show consistent twist and writhe signs, indicating a unified magnetic structure.

A possible scaling law exists between flare index and maximum umbral area.

Abstract

The emergence and magnetic evolution of solar active regions (ARs) of beta-gamma-delta type, which are known to be highly flare-productive, were studied with the 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 beta-gamma-delta ARs can be classified into three topological types as "quasi-beta", "writhed" and "top-to-top". ii) Among them, 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 beta-gamma-delta AR are not separated but united as a single structure below the solar surface. iv) Almost all the "writhed"-type ARs have downward knotted structures in the mid portion of the magnetic flux tube. This, we believe, is the essential property of beta-gamma-delta ARs. v) The flare activity of beta-gamma-delta 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.