Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006apjs..166..378p&link_type=abstract
The Astrophysical Journal Supplement Series, Volume 166, Issue 1, pp. 378-409.
Astronomy and Astrophysics
Astronomy
7
Magnetohydrodynamics: Mhd, Sun: Corona, Sun: Magnetic Fields
Scientific paper
The solar coronal plasma is too hot and too highly conducting thermally to be static in the absence of powerful inward forces. Sufficiently strong and closed magnetic field configurations do, however, contain the plasma in the low corona in spite of its high temperature. Very many of these closed loop structures, with greatly varying physical characteristics, coexist in quasi-static mutual equilibrium in the corona. We model three-dimensional (3D) loop systems by horizontally stacking many diverse loops into a 3D equilibrium solution, where individual loops are separated from each other by tangential discontinuities. Simulated narrowband filter images of this solution reproduce the filamentary appearance of loop systems familiar from observations. A simple 3D time-dependent model of horizontal shearing motions is also presented. We then investigate the dissipation and field reconnection across these tangential discontinuities that must form spontaneously in coronal magnetic fields. The postdiffusion dynamics are dictated by the outward cross-field gas pressure gradient forces, which are increasing functions of pressure and temperature. Thus, in isothermal systems a net plasma outflow results from each field diffusion, while in nonisothermal systems relatively hot loops tend to expand as a result of field diffusion processes, which may allow hot plasma ultimately to escape into the solar wind. Accompanying cool downflows predicted by the calculations may be identified with observed persistent mass downflows in active region loops in cool coronal lines. In addition, current sheet dissipation in a sheared loop system may create field-aligned counterflow patterns in neighboring loops, a phenomenon that has also been observed.
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