Physics
Scientific paper
Jan 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990phdt........39p&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF WISCONSIN - MADISON, 1990.Source: Dissertation Abstracts International, Volume: 51-09, Sectio
Physics
Scientific paper
The effects of equilibrium mass flow on the propagation characteristics of magnetohydrodynamic waves in solar coronal loops are investigated. These studies are motivated by the desire to improve current theories of coronal heating based on dissipation of Alfven waves. A challenge emerging from studies of solar phenomena is to explain the elevated coronal temperature. Many researchers now feel that Alfven wave heating may be the dominant coronal heating mechanism, but theories of such heating are not fully developed. In particular, contrary to observations, most Alfven wave heating theories assume that coronal plasmas are stationary and linear. However, equilibrium flow can significantly alter the spectral characteristics of wave phenomena and modify the linear and nonlinear stability of plasma structures. Coronal loops are magnetic flux tubes which connect regions of opposite magnetic polarity on the photosphere. Plasma within the loops is largely restricted to move along the length of the loop. The aligned flow model, characterized by the condition v_{rm o} = beta B_{rm o }, has been used to investigate the spectral properties of Alfven waves in coronal loops. We have explored flow effects on: (i) the characteristics of the shear Alfven wave continuum, (ii) linear and nonlinear stability of shear Alfven waves, and (iii) phase-mixing of surface waves in the presence of localized shear Alfven wave resonances on magnetic surfaces. Plasma flow emerges as a possibly stabilizing agent which may contribute to the observed long lifetime of coronal structures. Flow may strongly influence coronal heating in two direct ways. First, flow modifies the location and width of the shear Alfven wave continuum. Optimum absorption of shear Alfven waves in the corona requires that the driving frequency, determined by photospheric convection, lie in the flow-shifted continua. In addition, flow alters the damping rate of surface waves propagating along coronal loops. Additional effects which are commonly neglected in coronal loop studies are magnetic field curvature and solar gravity. As an initial step toward a realistic formulation of magnetohydrodynamic wave phenomena in coronal loops, we have explored the topology of multi-dimensional coronal loop equilibria in the presence of mass flow, magnetic curvature and solar gravity.
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