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The coronal energy input from magnetic braiding.

Yeates, A. R. and Bianchi, F. and Welsh, B. T. and Bushby, P. J. (2014) 'The coronal energy input from magnetic braiding.', Astronomy & astrophysics., 564 . A131.

Abstract

We estimate the energy input into the solar corona from photospheric footpoint motions, using observations of a plage region by the Hinode Solar Optical Telescope. Assuming a perfectly ideal coronal evolution, two alternative lower bounds for the Poynting flux are computed based on field line footpoint trajectories, without requiring horizontal magnetic field data. When applied to the observed velocities, a bound based solely on displacements between the two footpoints of each field line is tighter than a bound based on relative twist between field lines. Depending on the assumed length of coronal magnetic field lines, the higher bound is found to be reasonably tight compared with a Poynting flux estimate using an available vector magnetogram. It is also close to the energy input required to explain conductive and radiative losses in the active region corona. Based on similar analysis of a numerical convection simulation, we suggest that observations with higher spatial resolution are likely to bring the bound based on relative twist closer to the first bound, but not to increase the first bound substantially. Finally, we put an approximate upper bound on the magnetic energy by constructing a hypothetical "unrelaxed" magnetic field with the correct field line connectivity.

Item Type:Article
Keywords:Sun: corona, Sun: granulation, Sun: magnetic fields, Sun: photosphere.
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1051/0004-6361/201323276
Publisher statement:Credit: A. R. Yeates, F. Bianchi, B. T. Welsch, P. J. Bushby, A&A, 564, A131, 2014, reproduced with permission, © ESO.
Date accepted:No date available
Date deposited:14 April 2014
Date of first online publication:April 2014
Date first made open access:No date available

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