The Role of Twist in Kinked Flux Rope Emergence and Delta-spot Formation

• Published in: The Astrophysical journal 2018-09, Vol.864 (1), p.89
• Main Authors: Knizhnik, K. J., Linton, M. G., DeVore, C. R.
• Format: Article
• Language: English
• Subjects: Aerospace environments; Astrophysics; Computer simulation; Convection; Corona; Emergence; Fluctuations; Magnetic flux; Model testing; Photosphere; Polarity; Solar flares; Space weather; Sun: magnetic fields; Sun: photosphere; Sunspots; Weather
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aad68c

It has been observationally well established that the magnetic configurations most favorable for producing energetic flaring events reside in δ-spots, a class of sunspots defined as having opposite-polarity umbrae sharing a common penumbra. They are frequently characterized by extreme compactness, strong rotation, and anti-Hale orientation. Numerous studies have shown that nearly all of the largest solar flares originate in δ-spots, making the understanding of these structures a fundamental step in predicting space weather. Despite their important influence on the space environment, surprisingly little is understood about the origin and behavior of δ-spots. In this paper, we perform a systematic study of the behavior of emerging flux ropes to test a theoretical model for the formation of δ-spots: the kink instability of emerging flux ropes. We simulated the emergence of highly twisted, kink-unstable flux ropes from the convection zone into the corona, and we compared their photospheric properties to those of emerged weakly twisted, kink-stable flux ropes. We show that the photospheric manifestations of the emergence of highly twisted flux ropes closely match the observed properties of δ-spots, and we discuss the resulting implications for observations. Our results strongly support and extend previous theoretical work that suggested that the kink instability of emerging flux ropes is a promising candidate to explain δ-spot formation, as it reproduces their key characteristics very well.