The Observational Uncertainty of Coronal Hole Boundaries in Automated Detection Schemes

Martin A Reiss,Charles N Arge,Robert Jarolim,Alexander Kosovichev,Larisza Krista,Peter J Macneice,Rachel Bailey,Chris Lowder,Karin Muglach,Astrid Veronig,Stefan Hofmeister,Tadhg M Garton,Sangwoo Lee,Michael S F Kirk,Christian Möstl,Egor Illarionov,Véronique Delouille,Amr Hamada

doi:10.3847/1538-4357/abf2c8

Abstract

Abstract Coronal holes are the observational manifestation of the solar magnetic field open to the heliosphere and are of pivotal importance for our understanding of the origin and acceleration of the solar wind. Observations from space missions such as the Solar Dynamics Observatory now allow us to study coronal holes in unprecedented detail. Instrumental effects and other factors, however, pose a challenge to automatically detect coronal holes in solar imagery. The science community addresses these challenges with different detection schemes. Until now, little attention has been paid to assessing the disagreement between these schemes. In this COSPAR ISWAT initiative, we present a comparison of nine automated detection schemes widely applied in solar and space science. We study, specifically, a prevailing coronal hole observed by the Atmospheric Imaging Assembly instrument on 2018 May 30. Our results indicate that the choice of detection scheme has a significant effect on the location of the coronal hole boundary. Physical properties in coronal holes such as the area, mean intensity, and mean magnetic field strength vary by a factor of up to 4.5 between the maximum and minimum values. We conclude that our findings are relevant for coronal hole research from the past decade, and are therefore of interest to the solar and space research community.

Highlights

Coronal holes are an observational manifestation of open magnetic field lines emerging from the solar photosphere into interplanetary space
For the EUV data we focus on the mean intensity in the Atmospheric Imaging Assembly (AIA) 19.3 nm waveband (I193) which is the average intensity of all pixels inside the CH boundary given in data numbers (DNs) per second
The use of automated schemes for coronal hole detection is of critical importance for delineating the solar magnetic field that is open to the heliosphere

Summary

Introduction

Coronal holes are an observational manifestation of open magnetic field lines emerging from the solar photosphere into interplanetary space. Depending on the location and strength of the heating along the open field lines, several types of solar wind originate from coronal holes (McComas et al 2007). Because the open field guides coronal plasma into space, coronal holes are cooler and less dense than closed-field regions. The spectrum includes radio, near-infrared ( He I 1083 nm), white light, EUV, and X-rays (see Newkirk 1967; Munro & Withbroe 1972) Due to these collective observations and advancements in instrumentation and remote sensing, coronal hole research has flourished over the past decades. This research has covered plasma and magnetic properties (Zirker 1977; Cranmer 2009), temporal and spatial evolution, and the role played by coronal holes in modeling and predicting the ambient solar wind at Earth (Wang & Sheeley 1990; Riley et al 2001; Arge et al 2003)

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Results

Conclusion