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

TL;DR

This study introduces a synoptic map assimilation method to analyze the global rearrangements of open magnetic flux and the formation of polar coronal holes during Solar Cycle 24, revealing cause-effect relations and hemispheric asymmetries.

Contribution

The paper presents a novel method for studying magnetic flux rearrangements and correlates coronal hole formation with active complex decay, explaining hemispheric differences in polar coronal hole development.

Findings

Asynchronous polar coronal hole formation explained by magnetic flux decay.

North polar coronal hole formed later due to magnetic field complexity.

Large active complexes influence the formation and structure of coronal holes.

Abstract

A method of synoptic map assimilation has been developed to study global rearrangements of open magnetic flux and formation of polar coronal holes (PCHs) in the current cycle. The analysis reveals ensembles of coronal holes (ECHs) which appear within unipolar magnetic regions associated with decaying activity complexes (ACs). The cause-effect relations between them explain asynchronous PCH formation observed at the northern and southern hemispheres of the Sun. Thus, the decay of large ACs, that were observed in 2014, led to formation of an extensive ECH, which then became the south PCH in mid-2015. Intricate structure of magnetic fields in the northern polar zone has impeded the north PCH formation, despite the fact that the dominant polarity at the North Pole reversed two years earlier than at the South Pole. The north PCH formed only by mid-2016 as the result of gradual merger of high-latitudinal ECHs associated with several decaying ACs.