The Association of Filaments, Polarity Inversion Lines, and Coronal Hole Properties with the Sunspot Cycle: An Analysis of the McIntosh Database

TL;DR

This study analyzes the cyclic behavior and spatial evolution of solar filaments, PILs, and coronal holes over multiple solar cycles, revealing their correlation with the magnetic cycle and pole-ward migration patterns.

Contribution

It provides a comprehensive analysis of filament, PIL, and coronal hole properties across four solar cycles using the McIntosh archive, highlighting their relation to the solar magnetic cycle and polarity reversals.

Findings

Filament length, PIL length, and coronal hole area show cyclic behavior aligned with the solar magnetic cycle.

Filaments exhibit butterfly-like spatial distribution and pole-ward migration during cycle maxima.

Hemispheric asymmetries in filaments and PILs are positively correlated with sunspot area asymmetry.

Abstract

Filaments and coronal holes, two principal features observed in the solar corona are sources of space weather variations. Filament formation is closely associated with polarity inversion lines (PIL) on the solar photosphere which separate positive and negative polarities of the surface magnetic field. The origin of coronal holes is governed by large-scale unipolar magnetic patches on the photosphere from where open magnetic field lines extend to the heliosphere. We study properties of filaments, PILs and coronal holes in solar cycles 20, 21, 22 and 23 utilizing the McIntosh archive. We detect a prominent cyclic behavior of filament length, PIL length, and coronal hole area with significant correspondence with the solar magnetic cycle. The spatio-temporal evolution of the geometric centers of filaments shows a butterfly-like structure and distinguishable pole-ward migration of long filaments during cycle maxima. We identify this rush to the poles of filaments to be co-temporal with the initiation of polar field reversal as gleaned from Mount Wilson and Wilcox Solar Observatory polar field observations and quantitatively establish their temporal correspondence. We analyze the filament tilt angle distribution to constrain their possible origins. Majority of the filaments exhibit negative and positive tilt angles in the northern and the southern hemispheres, respectively -- strongly suggesting that their formation is governed by the overall large-scale magnetic field distribution on the solar photosphere and not by the small-scale intra-active region magnetic field configurations. We also investigate the hemispheric asymmetry in filaments, PILs, and coronal holes. We find that the hemispheric asymmetry in filaments and PILs are positively correlated -- whereas coronal hole asymmetry is uncorrelated -- with sunspot area asymmetry.