Physics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........20p&link_type=abstract
PhD Dissertation, Stanford Univ. CA United States
Physics
Solar Corona, Coronal Loops, Plasma Heating, Wave Propagation, Viscous Damping, Plasma Waves, Wave Dispersion, X Ray Telescopes, Japanese Spacecraft, Energy Dissipation, Viscosity, Thermal Conductivity, Transmission Loss, Plasma Density, Surface Waves, Power Spectra, Propagation Modes, Solar Magnetic Field, Frequency Ranges, Plasma Temperature
Scientific paper
The possible role of waves in the heating of the solar corona has been investigated. A dispersion relation has been derived for waves propagating in a homogeneous plasma subject to dissipation by viscosity and thermal conduction. The dissipation mechanisms have been incorporated self-consistently into the equations, and no assumptions about the strength of the damping have been made. Solutions of the sixth-order dispersion relation provide information on how the damping of both slow and fast mode waves depends upon various plasma parameters. It is shown that slow mode waves with periods less than about 300 seconds and fast mode waves with periods less than about 75 seconds can damp sufficiently rapidly to balance radiation losses in quiet regions. For active region conditions, slow mode waves with periods less than about 100 seconds may provide adequate heating. However, only fast mode waves of very high frequencies (tau is less than or equal to 1 s) can damp rapidly enough to balance the radiation loss rate in active regions. The homogeneous assumption is then relaxed to include a density stratification in a direction perpendicular to the uniform background magnetic field. Viscosity is incorporated self-consistently into the derivation, a slab model is adopted, and the viscous damping of the modes of the system, which are body waves and surface waves, is investigated. It is found that, while surface waves exhibit very small damping, body waves are able to damp sufficiently rapidly to balance radiation losses under active region conditions, provided that their frequencies are high enough. For example the wave frequency must be at least 5.0 s-1 for a slab density of 109.5 cm-3, a slab temperature of 106.5 K, and a field strength of 100 G. A tie-in with observations is then presented. Approximately 50 non-flaring coronal loops observed by the Soft X-Ray Telescope on the Yohkoh satellite have been analyzed. A power-law relationship between loop pressure and loop length, L, is determined, and this places important constraints on coronal heating theories. Specifically, it was found that the volumetric heating rate varies roughly as L-2.
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