Multi-Mode Kink Instability as a Mechanism for δ-Spot Formation
δ-spot active regions are a special class of active regions where a sunspot umbra of opposite polarity exist within the same penumbra (Zirin 1988). It is commonly held that active regions are the manifestation in the photosphere of a magnetic flux tube which arches up into the corona from the convection zone. The two opposite polarity spots of a bipolar active region are created by the intersection with the photosphere of the two legs of this arched flux tube. The close proximity of the opposite polarity spots of a δ-spot active region indicate that something forces the legs of the flux tube to remain close together. Other commonly observed properties of δ-spots, namely that the two spots rotate about each other as they evolve and that they develop magnetic shear along the magnetic neutral line between them, indicate that these active regions may be caused by kinked flux tubes, as first suggested by Tanaka (1991).
KeywordsActive Region Flux Tube Convection Zone Naval Research Laboratory Magnetic Flux Tube
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