Other
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........23h&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF COLORADO AT BOULDER, 1995.Source: Dissertation Abstracts International, Volume: 57-02, Section: B,
Other
2
Magnetism, Gravity Waves
Scientific paper
I explore the use of p-mode surface velocities and eigenfrequencies as diagnostics of solar magnetism. I investigate modifications produced by magnetic fields with two different geometries: a uniform vertical magnetic: field and a horizontal field sans shear. For the vertical field models, I use an adiabatically stratified polytrope to represent the solar interior. This polytrope is either complete or it is truncated with an isothermal chromosphere overlaid. For the complete polytrope, I analytically calculate the eigenfrequencies and eigenfunctions in the weak-field limit. For the truncated models, I include a spatially distributed driver of magnetosonic waves and solve the inhomogeneous problem numerically. For all vertical magnetic fields, I find extremely small frequency shifts. With magnetic fields of several hundred gauss in strength, typical shifts are on the order of a few nanohertz. Additionally, the damping provided by the conversion of acoustic energy into magnetic slow modes is exceptionally inefficient, and cannot explain the observed absorption of acoustic waves by sunspots and plage. I generate the solar models with a horizontal magnetic field by self consistently including magnetic forces in the equations of stellar structure. The p-mode frequency shifts produced by the horizontal magnetic field are roughly three order of magnitude larger than those induced by the vertical field. Furthermore, I find that in order to explain the observed suppression of p-mode surface velocities in active regions, the magnetic field cannot be localized in the vertical dimension. For both magnetic geometries, the surface amplitude of the acoustic field should depend on propagation direction, causing a modulation in power as a function of azimuth in a p-mode ring diagram. I search for such a surface velocity anisotropy in a data set which has an active region in its field-of-view. I find that there is a tendency for more power to propagate perpendicular to the active region's magnetic axis than along this axis. In addition, this anisotropy grows with field strength and lacks frequency dependence.
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