Is the Quiet-Sun Corona a Quasi-steady, Force-free Environment?

Details Is the Quiet-Sun Corona a Quasi-steady, Force-free Environment? Is the Quiet-Sun Corona a Quasi-steady, Force-free Environment?

Sep 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005apj...630..552s&link_type=abstract

The Astrophysical Journal, Volume 630, Issue 1, pp. 552-560.

Astronomy and Astrophysics

Astronomy

21

Sun: Corona, Sun: Magnetic Fields

Scientific paper

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 FH=8×1014B/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 β of gas to magnetic pressure lies close to unity throughout the modeled coronal height range of 22 Mm, with β>1 in ~30% of the volume and β>0.4 in ~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 β 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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