The Coronal Veil. (arXiv:2106.14877v2 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Malanushenko_A/0/1/0/all/0/1">A. Malanushenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cheung_M/0/1/0/all/0/1">M.C.M. Cheung</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+DeForest_C/0/1/0/all/0/1">C.E. DeForest</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Klimchuk_J/0/1/0/all/0/1">J.A. Klimchuk</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rempel_M/0/1/0/all/0/1">M. Rempel</a>
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.
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.
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