Characterizing the Umbral Magnetic Knots of δ-Sunspots

Abstract

Abstract Delta (δ) spots are active regions (ARs) in which positive and negative umbrae share a penumbra. They are known to be the source of strong flares. We introduce a new quantity, the degree of δ (Doδ), to measure the fraction of umbral flux participating in the δ-configuration and to isolate the dynamics of the magnetic knot, i.e., adjacent umbrae in the δ-configuration. Using Helioseismic and Magnetic Imager data, we analyze 19 δ-spots and 11 β-spots in detail, as well as 120 δ-spots in less detail. We find that δ-regions are not in a δ-configuration for the entire time but spend 55% of their observed time as δ-spots with an average, maximum Doδ of 72%. Compared to β-spots, δ-spots have 2.6× the maximum umbral flux, 1.9× the flux emergence rate, 2.6× the rotation, and 72× the flare energy. On average, the magnetic knots rotate 17° day−1, while the β-spots rotate 2° day−1. Approximately 72% of the magnetic knots present anti-Hale or anti-Joy tilts, contrasting starkly with only 9% of the β-spots. A positive correlation exists between ϕ Doδ and the flare energy emitted by that region. The δ-spots obey the hemispheric current helicity rule 64% of the time. A total of 84% of the δ-spots are formed by single flux emergence events, and 58% have a quadrupolar magnetic configuration. The δ-spot characteristics are consistent with the formation mechanism signatures as follows: 42% with the kink instability or Sigma effect, 32% with multisegment buoyancy, 16% with collisions, and two ARs that are unclassified but consistent with a rising O-ring.