Intermediate degree p-mode frequency splittings near solar maximum

Details Intermediate degree p-mode frequency splittings near solar maximum Intermediate degree p-mode frequency splittings near solar maximum

Jan 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994soph..149....1r&link_type=abstract

Solar Physics (ISSN 0038-0938), vol. 149, no. 1, p. 1-21

Physics

7

Calcium, Convection Cells, Frequency Shift, K Lines, Solar Activity, Solar Magnetic Field, Solar Rotation, Splitting, Acoustic Velocity, Magnetohydrodynamic Waves, Perturbation, Photosphere, Solar Interior, Spherical Harmonics

Scientific paper

We report on observations of global solar Ca K-line intensity oscillations taken in May 1991 from Mees Solar Observatory, Hawaii. We measure p-mode frequency splittings for modes of spherical harmonic degrees between 20 and 129 averaged over the radial order of the modes. Our measurement of the antisymmetric component of the splittings is comparable with previous measurements and thus indicates a decrease in the latitudinal differential rotation with depth into the convection zone and the upper radiative zone. We find evidence for a 1% variation in the rotation rate of the upper convection zone roughly in phase with the solar activity cycle. 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. From the degree dependence of the symmetric component of the splittings, we find evidence for an aspherical fractional sound speed perturbation located at a depth of 0.85 +/- 0.05 solar radii. This perturbation has a magnitude of (delta c)/c approx. = +9 x 10-4 at the equator relative to the poles. Additionally, there is evidence for a near-surface aspherical sound speed perturbation of a smaller magnitude (delta c)/c approx. +4 x 10-4 at the equator relative to the poles. If an intense global magnetic field were 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 G would be required in the convection zone.

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