Coronal Hole Detection and Open Magnetic Flux

Abstract

Many scientists use coronal hole (CH) detections to infer open magnetic flux. Detection techniques differ in the areas that they assign as open, and may obtain different values for the open magnetic flux. We characterize the uncertainties of these methods, by applying six different detection methods to deduce the area and open flux of a near-disk center CH observed on 2010 September 19, and applying a single method to five different EUV filtergrams for this CH. Open flux was calculated using five different magnetic maps. The standard deviation (interpreted as the uncertainty) in the open flux estimate for this CH ≈ 26%. However, including the variability of different magnetic data sources, this uncertainty almost doubles to 45%. We use two of the methods to characterize the area and open flux for all CHs in this time period. We find that the open flux is greatly underestimated compared to values inferred from in situ measurements (by 2.2-4 times). We also test our detection techniques on simulated emission images from a thermodynamic MHD model of the solar corona. We find that the methods overestimate the area and open flux in the simulated CH, but the average error in the flux is only about 7%. The full-Sun detections on the simulated corona underestimate the model open flux, but by factors well below what is needed to account for the missing flux in the observations. Under-detection of open flux in coronal holes likely contributes to the recognized deficit in solar open flux, but is unlikely to resolve it.

An Electric-field-driven Global Coronal Magnetohydrodynamics Simulation Model Using Helioseismic and Magnetic Imager Vector-magnetic-field Synoptic Map Data

“…Furthermore, the steady-state solution can be used in simulations of coronal perturbation as the preperturbed state (e.g., Usmanov & Dryer 1995). In general the magneticfield structures of the PFSS solution as well as the MHDrelaxed states indeed agree well with observations of the solar corona, such as the off-limb coronal electron density measured by the coronagraphs and the shape of coronal holes seen in the short-wavelength observations (e.g., Riley et al 2019;Linker et al 2021) in the global scale.…”

Tracking Movement of Long-lived Equatorial Coronal Holes from Analysis of Long-term McIntosh Archive Data

“…Such diagrams have been brought up in solar studies, particularly in the context of solar Rossby waves detection, by McIntosh et al (2017), and have been used recently (see, e.g., Krista et al 2018). There are many approaches to the automated detection and characterization of coronal holes in EUV observations, such as CATCH (Heinemann et al 2019), CHIMERA (Garton et al 2017), SPOCA (Verbeeck et al 2013), CHARM (Krista & Gallagher 2009), CHORTLE (Lowder et al 2014), SYNCH (Hamada et al 2018), CHRONNOS (Jarolim et al 2021), as well as PSI-SYNCH and PSI-MIDM (see, e.g., Linker et al 2021). In this paper we do not identify the coronal holes per se; those were already mapped as part of the analysis required to construct the maps included in the McA (Hewins et al 2017).…”

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

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