Rings and trumpets - Three-dimensional power spectra of solar oscillations

When slices of characteristic 'trumpet' surfaces visible in three-dimensional power spectra of the Doppler shifts observed on the solar surface are taken at constant temporal frequency, the cross sections form 'rings'. Analysis of the shape and position of these rings provides information on the horizontal flow field and the thermodynamic structure below the photosphere. The relationship between the parameters of an elliptical approximation to the rings and the subphotospheric state is derived, and a numerical simulation is presented. A preliminary application to real data suggests the presence of a flow of 100 m/s directed from the equator toward the south pole. A comparison of the velocities inferred from a single ring obtained at different longitudes shows variations of 20-40 m/s, suggesting that large-scale convection is not azimuthally symmetric.

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