Physics
Scientific paper
Dec 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt.........6s&link_type=abstract
Thesis (PHD). UNIVERSITY OF MARYLAND COLLEGE PARK , Source DAI-B 59/06, p. 2826, Dec 1998, 116 pages.
Physics
Line Tying, Current Sheets
Scientific paper
Quasi-static frozen-in motions of magnetohydrodynamic plasma in the vicinity of immobile conductors are considered. The latter surfaces present 'line-tied' boundary conditions to the motions. The physical systems of interest are the Magnetosphere-Ionosphere-Atmosphere-Earth (MIE) system and the Solar-Corona-Photosphere system. For the MIE system, the effects of an intervening insulating atmosphere on frozen-in and 'line-tying' are examined. For the solar case, the existence of well-behaved neighboring equilibria is investigated. Four self-contained problems are solved and presented sequentially sequentially as follows: A one-dimensional model representing the MIE system is analyzed. Charged particle collisions as well as charged-neutral collisions are included in a detailed manner. We show that the layer of nonideal plasma near the conducting Earth does not significantly alter the line-tying of the magnetic field that would be expected from frozen-in considerations. An extension of the previous calculation to three dimensions is analyzed. This model comprises a spherical conducting Earth, an insulating atmosphere, and a frozen-in magnetosphere. Convective displacements are imposed in the magnetosphere and the resulting pattern of electromagnetic fields is solved for. It is shown that 'remnants' of the frozen-in solution can be recovered, under certain circumstances. In particular, for magnetospheric forcing with North-South asymmetry, terrestrial currents are driven which can be larger than ionospheric currents. Neighboring magnetic equilibria driven by quasi-static motions at the 'foot-points' of magnetic field lines dipping into the solar surface are examined. We show that the ordering underlying the 'reduced equations' of MHD breaks down at the solar surface. A boundary layer is uncovered. Reduced equations are derived for the layer and matched asymptotically to the outer equations. The boundary layer is, however, shown to be 'benign' in that the usual procedures using the reduced equations are not affected. We present two examples of simple foot-point motions that result in singular neighboring equilibria. These solutions contain spontaneously generated current sheet discontinuities, in support of a coronal heating scenario suggested by Parker. Our solutions are remarkable for the facts that the model is entirely two-dimensional, that there are no preexisting X-points, and that they are analytically transparent.
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