Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...463..784g&link_type=abstract
Astrophysical Journal v.463, p.784
Astronomy and Astrophysics
Astronomy
6
Magnetohydrodynamics: Mhd, Sun: Chromosphere, Sun: Magnetic Fields
Scientific paper
A two-dimensional, dissipative magnetohydrodynamic model is used to argue that a major source of in situ heating for the solar middle chromosphere is the resistive dissipation of large-scale electric currents flowing in magnetic elements. A magnetic element is an arch-shaped magnetic field configuration consisting of a central region of horizontally localized, mainly vertical magnetic field based in the photosphere, with field lines that diverge horizontally with increasing height, extend into the middle chromosphere, and then return to the photo sphere as a relatively diffuse, weaker field. The currents that flow in these elements are carried by protons, and are large scale in that their scale height is hundreds of kilometers in the network and thousands of kilometers in the internetwork. Solutions to the model demonstrate that the resistive dissipation of large-scale electric currents flowing orthogonal to the magnetic field in magnetic elements embedded in a weakly ionized, strongly magnetized hydrogen gas may generate all of the thermal energy necessary to heat the middle chromosphere. The magnetic field is computed self-consistently with the electric field, pressure, and hydrogen and proton densities. Solutions to the model suggest that magnetic elements with horizontal extents up to several arcseconds may be confined to, and heat, the chromospheric network, while elements with the largest horizontal extents may span and heat the internetwork and be the building blocks of the chromospheric magnetic canopy. The model predicts that the heating rate per unit mass (q) is independent of height, peaked near but horizontally displaced from the center of a magnetic element, and for realistic model input parameters has an average value computed over the base area of the element dose to the value 4.5 x 109 ergs g-1 s-1 predicted by semiempirical models of the chromosphere that also predict that q is independent of height in the middle chromosphere. The model predicts that the heating rate per unit volume is peaked near the horizontal midpoint of a magnetic element where the field is mainly horizontal. The model predicts that both heating rates are zero at the center and outer boundary of a magnetic element where the field is vertical. These model predictions for the spatial localization of the heating rates are consistent with observations that regions of enhanced emission are near but horizontally displaced from regions of vertical, high-magnitude magnetic field.
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