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P. Dmitruk, W. H. Matthaeus (Bartol Inst., U. Del.)
The solar corona is more than two orders of magnitude hotter than the Sun's surface. The implied heating mechanism accelerates the solar wind and establishes the boundary conditions for the entire plasma heliosphere. It has been proposed that the required energy, originating in photospheric motions, is transported to the corona through low-frequency MHD waves generated above the Sun's surface. A fundamental question to answer is how the energy found in those large-scales, low-frequency motions is transferred into small scales where it can be efficiently dissipated at altitudes commensurate with the observed heating of the corona and acceleration of the solar wind. An attractive idea is the development of MHD turbulence to fill that gap in scales. Here we discuss a coronal heating model based on a cascade to small transverse scales that is driven by low frequency waves or quasi static motions at the coronal base [1-3]. The conditions (on relevant timescales) that favor the development and sustainment of MHD turbulence in an open region will be discussed. The results are supported by numerical simulations of the MHD equations under assumption of a strong magnetic field and an inhomogeneous background density. A heating profile at distances below two solar radii can be derived from this model. Typical quasi-2D structures are formed with implications for dissipation mechanisms.
[1] W. Matthaeus, G. Zank, S. Oughton. D. Mullan and P Dmitruk, Astrophys. J, 523, L93 (1999)
[2] P. Dmitruk, W Matthaeus, L. Milano, S. Oughton, G. Zank and D. Mullan, Astrophys. J., 575, 571 (2002)
[3] P. Dmitruk and W Matthaeus, Astrophys. J., 597, 1097 (2003)
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Bulletin of the American Astronomical Society, 36 #2
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