The Observational Uncertainty of Coronal Hole Boundaries in Automated Detection Schemes

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.

Statistical Evidence for Small-scale Interchange Reconnection at a Coronal Hole Boundary

“…It is currently unknown if this is a problem with magnetographs themselves, as magnetic field readings are frequently non-uniform across various instruments (Riley et al 2014;Wallace et al 2019;Wang et al 2022). It could also be due to the highly complex structure of the low corona, coupled with observational limitations along a single line of sight, which both serve to obscure the physical open/closed boundary (Kirk et al 2009;Linker et al 2021;Reiss et al 2021), or even to misinterpretations of the in-situ open flux measurements (Frost et al 2022). This problem has driven an active research area devoted to determining CH boundaries as best we can using remote data (Aschwanden 2005;Esser 1999;Krista et al 2011;Garton et al 2018;Reiss et al 2021).…”

“…It could also be due to the highly complex structure of the low corona, coupled with observational limitations along a single line of sight, which both serve to obscure the physical open/closed boundary (Kirk et al 2009;Linker et al 2021;Reiss et al 2021), or even to misinterpretations of the in-situ open flux measurements (Frost et al 2022). This problem has driven an active research area devoted to determining CH boundaries as best we can using remote data (Aschwanden 2005;Esser 1999;Krista et al 2011;Garton et al 2018;Reiss et al 2021). There are practical motivations to constrain a definition that is both observationally detectable and physically motivated: the high-speed wind streams from CHs are among the most important drivers of space weather, and forecasters are routinely searching for ways to make arrival times more accurate.…”

SCSS-Net: Solar Corona Structures Segmentation by Deep Learning

“…In general, it will be very valuable if a master test dataset is created with correct and precise ground truth reference annotations that will be used as the main reference for benchmark of different approaches for segmentation of coronal structures. Indeed, this effort has already started as it is presented by Reiss et al (2021). Qualitatively, SCSS-Net provides comparable results of seg-mentation of coronal holes as methods used in this study.…”

Identification of Coronal Holes on AIA/SDO Images Using Unsupervised Machine Learning

“…Interestingly enough, our results show significant discrepancies between the identified CHs using our method, HEK, and CATCH when we look at the temporal variations in the correlation coefficients calculated for the total areas. Recently, some steps have been taken to create a reliable database where there is a consensus about the CH boundaries and their uncertainties are being discussed (Linker et al 2021;Reiss et al 2021).…”