4.7 Article

Is the quiet-sun corona a quasi-steady, force-free environment?

Journal

ASTROPHYSICAL JOURNAL
Volume 630, Issue 1, Pages 552-560

Publisher

IOP PUBLISHING LTD
DOI: 10.1086/431754

Keywords

sun : corona; sun : magnetic fields

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We model a coronal volume over a quiet, mixed-polarity solar network as an ensemble of quasi-steady loop atmospheres. These are contained by an assumed potential field, including the associated variations in the loop cross section through the coronal volume and the loop flows induced by such asymmetries. The average temperature and density stratifications are close to those of the quiet-Sun corona for a coronal heating flux density into the corona of F-H = 8 X 10(14)B/L (ergs cm(-2) s(-1)) for loop-base field strengths B ( G) and loop half-lengths L ( cm). Earlier, that heating parameterization was shown to be consistent with the appearance and radiative losses of a solar corona in which active regions dominated the emission. This study thus supports the hypothesis that the same, likely braiding-driven, heating dominates throughout the quiescent corona. The average ratio beta of gas to magnetic pressure lies close to unity throughout the modeled coronal height range of 22 Mm, with beta > 1 in similar to 30% of the volume and beta > 0: 4 in similar to 90% of the volume, perhaps indicating that the quiet-Sun corona is driven to near its maximum heating capacity by the random walk of its footpoints. Our findings that the solar corona has beta close to unity, and that our model corona exhibits insufficient fine structure and no significant spatially averaged Doppler shifts, imply that the quiet-Sun corona is often neither quasi-steady nor force free and thus that dynamic magnetohydrodynamics (MHD) models are essential to furthering our understanding of the quiet solar corona.

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