Phenomena in an Emerging Active Region. II. Properties of the Dynamic Small‐Scale Structure

Abstract

The magnetic flux emergence in growing active region NOAA 5617, when it is about 8 hr old, shows an intricate fine structure. The small-scale emergence events are characterized by a coincident upflow and transient darkening (of about 2 Mm and 10 minutes) in the continuum and line-center intensity followed by the appearance of one, or in some cases two, new bright grains flanking the line-center darkening. The bright grains (faculae) coincide with magnetic flux concentrations and downflows. The footpoints move apart at on average 1.4 km s-1. Flux emergence happens recurrently in a number of locations widely distributed over the active region, which appear to form a pattern with a wavelength of about 8 Mm. A preferred orientation that fits Hale's polarity law is displayed by the spatial pattern in the emergence locations, the emergence events themselves, subsequent footpoint motion, and the Hα arch filament system. We find long (~15 Mm) alignments of unipolar faculae of each magnetic polarity that also follow the preferred orientation. We adapt the model for flux emergence to accommodate the observed dynamic fine structure. Essential new features are (1) the emerging bundle of flux tubes is frayed in two systems, in vertical stacks, arranged in slightly curved, nearly parallel sheets; and (2) many flux tubes emerge in multiple locations.