Computer Science – Sound
Scientific paper
Sep 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........2r&link_type=abstract
Ph.D. Thesis Hawaii Univ., Honolulu.
Computer Science
Sound
7
K Lines, Line Spectra, Solar Cycles, Solar Oscillations, Solar Rotation, Convection, Latitude, Solar Activity
Scientific paper
We report on the results of extended observations of global solar oscillations as measured in the Ca K spectral line. We measure p-mode frequency splittings averaged over the radial order of the oscillations modes. Our measurement of the antisymmetric component of the splittings is consistent with previous measurements. We present an inversion for the internal rotation rate as a function of latitude and radius in the convection zone and upper radiative zone from the observed antisymmetric splittings. This inversion reveals a slight increase in the rotation rate at all latitudes going inward from the surface to about 0.9 solar radii. Below this depth there is a decrease in the rotation rate with depth. Latitudinal differential rotation persists throughout much of the convection zone but decreases near the base of the convection zone. Our measurement of the symmetric component of the splittings is of the same order as was reported from the previous solar maximum and is an order of magnitude larger than has been measured near solar minimum. We find evidence for an aspherical fractional sound speed perturbation located at a depth of 0.85 plus or minus 0.05 solar radii. This perturbation has a magnitude of delta c/c approx. equals +9 x 10-4 at the equator relative to the poles. If an internal global magnetic field is the dominant source of the observed symmetric component of the splittings instead of latitudinal gradients in the sound speed then global fields of order 105 Gauss would be required in the convection zone. We detect high frequency counterparts to the global p-mode oscillations up to frequencies of 10 mHz in the intermediate degree range. The peak frequencies of the high frequency spectrum and the p-mode eigenfrequencies obey the same dispersion relationship (Duvall's Law) which is derived for the p-mode acoustic cavity. The high frequency 'modes' have linewidths which are roughly constant with frequency.
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