Alfven Wave Model of Spicules and Coronal Heating

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Abstract

Magnetohydrodynamic simulations are performed for torsional Alfvén waves propagating along an open magnetic flux tube in the solar atmosphere. It is shown that, if the root mean square of the perturbation is greater than ~1 km s-1 in the photosphere, (1) the transition region is lifted up to more than ~5000 km (i.e., the spicule is produced), (2) the energy flux enough for heating the quiet corona (~3.0×105 ergs s-1 cm−2) is transported into the corona, and (3) nonthermal broadening of emission lines in the corona is expected to be ~20 km s-1. We assumed that the Alfvén waves are generated by random motions in the photosphere. As the Alfvén waves propagate upward in the solar atmosphere, longitudinal motions are excited by the nonlinear couplings. The longitudinal motions propagate upward as slow or fast waves and lift up the transition region (i.e., the spicule is produced). A part of the Alfvén waves are reflected in the transition region, but the remaining waves propagate upward to the corona and contribute both to the heating of the corona and the nonthermal broadening of emission lines. The result of our simulation would suggest that the quiet hot corona, nonthermal broadening of lines, and spicules are caused by Alfvén waves that are generated in the photosphere.

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