Hemispheric Preference and Cyclic Variation of Solar Filament Chirality from 2000 to 2016

TL;DR

This study analyzes the hemispheric preference and cyclic variation of solar filament chirality from 2000 to 2016, comparing manual and automated detection methods, and finds consistent hemispheric preferences across solar cycles with some discrepancies.

Contribution

It applies and compares automated and manual methods for determining filament chirality over multiple solar cycles, highlighting the consistency and challenges in automated detection.

Findings

83% of visually determined filaments follow hemispheric preference

58% of automated determinations follow hemispheric preference

Hemispheric preference remained consistent between solar cycles 23 and 24

Abstract

It is well known that solar filaments are features in the solar atmosphere which show a hemispheric preference in their chirality. The hemispheric preference is such that the dextral chirality dominates in the northern hemisphere while the sinistral chirality dominates in the southern. Determining the strength and cyclic variation of the degree of this hemispheric preference, however, is challenging and tedious and thus needs to be automated. In this paper, we follow Dr. Pietro Bernasconi's algorithm (Bernasconi et al. 2005) to detect filament chirality with two parallel channels of application. The algorithm is applied to H-alpha images by "Advanced Automated Filament Detection and Characterization Code" (AAFDCC) (Bernasconi et al. 2005) or the algorithm is explained to a human and the human determines the chirality of the solar filament. We have conducted this exercise on data during the month of August from years 2000 to 2016 and we found that 83 % of our visually determined filaments follow the hemispheric chirality preference, while 58 % of automatically determined filaments follow it. Our visually compiled results have over 90 % agreement with those of Pevtsov et al. (2003), yet the visually determined chiralities of filaments disagree with automated determinations significantly. We find that the hemispheric preference remained the same between solar cycles 23 and 24 but the preference is very difficult to determine during the solar minimum of 2008-2010 primarily due to the absence of filaments.