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The Coronal Veil  

Anna Malanushenko   Submitted: 2021-02-14 22:29

The Sunís corona is dominated by magnetically confined structures, which appear in observations as coronal loops, whose major diameters are hundreds to thousands of kilometers. Loop features are readily seen in all images of the solar corona, and are commonly understood to be caused by magnetically confined flux tubes that have compact cross sections. This basic interpretation leads to several important difficulties in understanding of the solar corona: constant cross section of loops and their anomalously high density scale height.We explore the 3D thermodynamic structure of plasma above an active region in an MHD simulation of a full active region in an attempt to find volume counterparts for coronal loops. Our our finding is that in many cases, a coronal loop cannot be linked to an individual bright strand in the volume. While many thin loops are present in the synthetic images, the bright structures in the volume are fewer, and are of remarkably complex shape. We demonstrate how the complexity of these shapes could be responsible for forming impressions of isolated thin bright coronal loops, even in the absence of thin bright plasma strands. We argue that it is difficult to tell from an observation whether a particular loop corresponds to a strand in the volume or whether it is a projection artifact. We demonstrate how the apparent isolation of a loop could be deceiving the observers, even when observations from two viewing angles are available.While we base our supporting analysis on 3D data cubes from a radiative magnetohydrodynamic (MHD) simulation, the purpose of this study is not to compare or validate this particular simulation against observations. We use these data to illustrate how a combination of complex temperature and density distributions and line-of-sight integration can lead to the appearance of loop like features in synthetic emission even if the 3D volume data does not contain compact density and temperature structures itself. The main findings of our analysis are independent from a particular simulation setup and simply illustrate the intrinsic complexity involved in interpreting observations that result from line-of-sight integration in an optically thin plasma.

Authors: A. Malanushenko, M.C.M. Cheung, C.E. DeForest, J.A. Klimchuk, M. Rempel

Publication Status: ApJ, in preparation
Last Modified: 2021-06-23 03:10
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Using Coronal Loops to Reconstruct the Magnetic Field of an Active Region Before and After a Major Flare  

Anna Malanushenko   Submitted: 2013-12-18 16:37

The shapes of solar coronal loops are sensitive to the presence of electrical currents that are the carriers of the nonpotential energy available for impulsive activity. We use this information in a new method for modeling the coronal magnetic field of AR 11158 as a nonlinear force-free field (NLFFF). The observations used are coronal images around time of major flare activity on 2011/02/15, together with the surface line-of-sight magnetic field measurements. The data are from the Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly (HMI and AIA, respectively) onboard the Solar Dynamics Observatory (SDO). The model fields are constrained to approximate the coronal loop configurations as closely as possible, while also subject to the force-free constraints. The method does not use transverse photospheric magnetic field components as input, and is thereby distinct from methods for modeling NLFFFs based on photospheric vector magnetograms. We validate the method using observations of AR 11158 at a time well before major flaring, and subsequently review the field evolution just prior to and following an X2.2 flare and associated eruption. The models indicate that the energy released during the instability is about 1 imes1032 erg, consistent with what is needed to power such a large eruptive flare. Immediately prior to the eruption the model field contains a compact sigmoid bundle of twisted flux that is not present in the post-eruption models, which is consistent with the observations. The core of that model structure is twisted by approx0.9 full turns about its axis.

Authors: A. Malanushenko, C. Schrijver, M. L. DeRosa, M. S. Wheatland

Publication Status: ApJ (accepted)
Last Modified: 2013-12-19 07:43
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The Coronal Veil
Using Coronal Loops to Reconstruct the Magnetic Field of an Active Region Before and After a Major Flare

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