Decay of Activity Complexes, Formation of Unipolar Magnetic Regions, and Coronal Holes in Their Causal Relation

Abstract

North-south asymmetry of sunspot activity resulted in an asynchronous reversal of the Sun's polar fields in the current cycle. The asymmetry is also observed in the formation of polar coronal holes. A stable coronal hole was first formed at the South Pole, despite the later polar-field reversal there. The aim of this study is to understand processes making this situation possible. Synoptic magnetic maps from the Global Oscillation Network Group and corresponding coronal-hole maps from the Extreme ultraviolet Imaging Telescope aboard the Solar and Heliospheric Observatory and the Atmospheric Imaging Assembly aboard the Solar Dynamics Observatory are analyzed here to study a causal relationship between the decay of activity complexes, evolution of largescale magnetic fields, and formation of coronal holes. Ensembles of coronal holes associated with decaying active regions and activity complexes are presented. These ensembles take part in global rearrangements of the Sun's open magnetic flux. In particular, the south polar coronal hole was formed from an ensemble of coronal holes that originated after the decay of multiple activity complexes observed during 2014.

Rearrangements of Open Magnetic Flux and Formation of Polar Coronal Holes in Cycle 24

“…Clearly, according to the differential rotation profile, the surges at mid-latitudes are inclined equatorward at an angle which is greater than those observed at high latitudes. Previously, Golubeva and Mordvinov (2016) noted that the high-latitudinal surges of negative polarity formed due to the decay of pre-existing ACs, then formed a ring structure around the South Pole during their meridional transport and finally caused the change of dominant polarity at the South Pole. Figure 1b shows the averaged CH distribution for MCR 2151.…”

“…It is also clear that the ECHs usually formed near the major long-lived ACs, or the nests of activity (Golubeva and Mordvinov, 2016). Figure 1c presents the superposition of distributions given in Figures 1a and 1b, and the neutral-line position on the source surface at 2.5 solar radius for Blue contours correspond to magnetic field of 1 G, and red contours to -1 G. The fields greater than 10 G are in blue, and the fields less than -10 G are in red.…”