Evolution and Flare Activity of Delta-Sunspots in Cycle 23

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.

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• Successive flux rope eruptions from $\delta$-Sunspots region of NOAA 12673 and associated X-class eruptive flares on 2017 September 6
• Numerical Study on Emergence of Kinked Flux Tube for Understanding of Possible Origin of Delta-spot Regions
• Differences in the solar cycle variability of simple and complex active regions during 1996-2018
• Different contributions to space weather and space climate from different big solar active regions
• Applying the weighted horizontal magnetic gradient method to a simulated flaring Active Region
• The configuration and failed eruption of a complex magnetic flux rope above a δ sunspot region
• Characterizing the Umbral Magnetic Knots of $\delta$-Sunspots