The Coronal Veil

Abstract

Coronal loops, seen in solar coronal images, are believed to represent emission from magnetic flux tubes with compact cross-sections. We examine the 3D structure of plasma above an active region in a radiative magnetohydrodynamic simulation to locate volume counterparts for coronal loops. In many cases, a loop cannot be linked to an individual thin strand in the volume. While many thin loops are present in the synthetic images, the bright structures in the volume are fewer, and of complex shape. We demonstrate that this complexity can form impressions of thin bright loops, even in the absence of thin bright plasma strands. We demonstrate the difficulty of discerning from observations whether a particular loop corresponds to a strand in the volume, or a projection artifact. We demonstrate how apparently isolated loops could deceive observers, even when observations from multiple viewing angles are available. While we base our analysis on a simulation, the main findings are independent from a particular simulation setup and illustrate the intrinsic complexity involved in interpreting observations resulting from line-of-sight integration in an optically thin plasma. We propose alternative interpretation for strands seen in EUV images of the corona. The "coronal veil" hypothesis is mathematically more generic, and naturally explains properties of loops that are difficult to address otherwise -- such as their constant cross section and anomalously high density scale height. We challenge the paradigm of coronal loops as thin magnetic flux tubes, offering new understanding of solar corona and, by extension, of other magnetically confined bright, hot plasmas.

ApJ (in press)

References in corpus (8)

• Key Aspects of Coronal Heating
• Extension of the MURaM radiative MHD code for coronal simulations
• Fine strand-like structure in the solar corona from MHD transverse oscillations
• Are constant loop widths an artifact of the background and the spatial resolution?
• On the Area Expansion of Magnetic Flux-Tubes in Solar Active Regions
• Magnetic field diagnostics and spatio-temporal variability of the solar transition region
• Multi-spacecraft observations of coronal loops to verify a force-free field reconstruction and infer loop cross sections
• A Comparison of EIT and TRACE Loop Widths

Cited by in corpus (17)

• Defining the Middle Corona
• Magnetic Tornado Properties: A Substantial Contribution to the Solar Coronal Heating via Efficient Energy Transfer
• Prevalence of Thermal Non-Equilibrium over an Active Region
• EUV fine structure and variability associated with coronal rain revealed by Solar Orbiter/EUI HRIEUV and SPICE
• A model for heating the super-hot corona in solar active regions
• Swirls in the Solar Corona
• Stereoscopic observations reveal coherent morphology and evolution of solar coronal loops
• Electron Weibel instability and~quasi-magnetostatic structures in~an~expanding collisionless plasma
• Can we rely on EUV emission to identify coronal waveguides?
• The Equilibrium of Coronal Loops Near Separatrices
• Magnetic Energy Powers the Corona: How We Can Understand its 3D Storage & Release
• On the intermittency of hot plasma loops in the solar corona
• Damping of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere
• Source location and evolution of a multi-lane type II radio burst
• Long-lived coronal loops in solar active regions
• Data-driven Radiative Magnetohydrodynamics Simulations with the MURaM Code: Coronal Heating and Dynamics in an Emerging Active Region
• Validation & Testing of the CROBAR 3D Coronal Reconstruction Method with a MURaM simulation