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Title: Gravitational steady states of solar coronal loops

Authors:
ORCiD logo [1]; ORCiD logo [2]
  1. Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
  2. Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1349339
Grant/Contract Number:
SC0007883
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 2; Related Information: CHORUS Timestamp: 2018-02-14 12:24:58; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics
Country of Publication:
United States
Language:
English

Citation Formats

Sugiyama, Linda E., and Asgari-Targhi, M.. Gravitational steady states of solar coronal loops. United States: N. p., 2017. Web. doi:10.1063/1.4975311.
Sugiyama, Linda E., & Asgari-Targhi, M.. Gravitational steady states of solar coronal loops. United States. doi:10.1063/1.4975311.
Sugiyama, Linda E., and Asgari-Targhi, M.. Wed . "Gravitational steady states of solar coronal loops". United States. doi:10.1063/1.4975311.
@article{osti_1349339,
title = {Gravitational steady states of solar coronal loops},
author = {Sugiyama, Linda E. and Asgari-Targhi, M.},
abstractNote = {},
doi = {10.1063/1.4975311},
journal = {Physics of Plasmas},
number = 2,
volume = 24,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.4975311

Citation Metrics:
Cited by: 1work
Citation information provided by
Web of Science

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  • In this work, the well established two-fluid relaxation model based on the minimum energy principle is extended to include open systems like the solar corona. The Euler-Lagrange equations obtained are of double curl in nature and support non-zero plasma-{beta} along with mass flow of the magnetofluid. These equations are solved in Cartesian coordinates utilizing a geometry relevant to the solar atmosphere, and a basic comparative study of the non force-free, force-free, and potential magnetic field obtained as solutions of the same Euler-Lagrange equations is presented.
  • Siphon flow in hot coronal loops is examined, in both its steady and dynamic states, in the latter case using a flux-corrected transport simulation. We find that such flows are inhibited by (1) low heating rates, (2) high pressures, (3) short loop lengths, and (4) turbulence. In accordance with expectations, we find that small footpoint pressure asymmetries produce steady subsonic flow. However, the standard picture that larger values yield standing shocks is shown to be valid only for sufficiently high heating, long loops, or low pressure. Values of these parameters more characteristic of active regions produce instead a quasi-periodic surgemore » flow when the pressure asymmetry exceeds a critical value at which the temperature gradient at the inflow end reverses sign. These flows are normally subsonic, though examples can be found where the surge is supersonic for a part of each period. The difficulty of driving substantial siphon flows for realistic hot loop models is in accordance with the comparative rarity of observations of these flows. 37 refs.« less
  • A previous work of ours found the best agreement between EUV light curves observed in an active region core (with evidence of super-hot plasma) and those predicted from a model with a random combination of many pulse-heated strands with a power-law energy distribution. We extend that work by including spatially resolved strand modeling and by studying the evolution of emission along the loops in the EUV 94 Å and 335 Å channels of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. Using the best parameters of the previous work as the input of the present one, we findmore » that the amplitude of the random fluctuations driven by the random heat pulses increases from the bottom to the top of the loop in the 94 Å channel and from the top to the bottom in the 335 Å channel. This prediction is confirmed by the observation of a set of aligned neighboring pixels along a bright arc of an active region core. Maps of pixel fluctuations may therefore provide easy diagnostics of nanoflaring regions.« less
  • Magnetic field extrapolation is an important tool to study the three-dimensional (3D) solar coronal magnetic field, which is difficult to directly measure. Various analytic models and numerical codes exist, but their results often drastically differ. Thus, a critical comparison of the modeled magnetic field lines with the observed coronal loops is strongly required to establish the credibility of the model. Here we compare two different non-potential extrapolation codes, a nonlinear force-free field code (CESE–MHD–NLFFF) and a non-force-free field (NFFF) code, in modeling a solar active region (AR) that has a sigmoidal configuration just before a major flare erupted from themore » region. A 2D coronal-loop tracing and fitting method is employed to study the 3D misalignment angles between the extrapolated magnetic field lines and the EUV loops as imaged by SDO /AIA. It is found that the CESE–MHD–NLFFF code with preprocessed magnetogram performs the best, outputting a field that matches the coronal loops in the AR core imaged in AIA 94 Å with a misalignment angle of ∼10°. This suggests that the CESE–MHD–NLFFF code, even without using the information of the coronal loops in constraining the magnetic field, performs as good as some coronal-loop forward-fitting models. For the loops as imaged by AIA 171 Å in the outskirts of the AR, all the codes including the potential field give comparable results of the mean misalignment angle (∼30°). Thus, further improvement of the codes is needed for a better reconstruction of the long loops enveloping the core region.« less
  • A basic assumption in the analysis of EUV and X-ray solar emission is that the plasma is in ionization equilibrium. The effects of mass flows on the ionization state of solar plasma have been investigated in order to check the validity of ionization equilibrium. Solar coronal loop models with a steady state flow as described by Antiochos (1984) are considered. The number densities of carbon ions have been determined for four loop models that cover a range of densities and flow velocities. The results show evidence of nonequilibrium ionization effects even for velocities of only a few km/s at themore » loop top and 10 times less at the base, with densities ranging from 10 to the 8th to 10 to the 10th/cu cm between the top and the footpoints. The importance of these results for the analysis of EUV and X-ray solar emission is discussed. 20 references.« less