Ring diagram parameter estimation and spectral model assumptions

Ring diagrams are used to study the structure and dynamics of the near-surface layers of the Sun. The parameters of primary interest are frequencies and velocities in both the zonal and meridional direction as a function of wavenumber and of radial order n. These parameters are recovered by fitting a model of the spectral profile to three-dimensional power spectra of small regions of the Sun. In addition to the spatial frequency and the zonal and meridional velocity components, our spectral model has ten free parameters. Using HMI resolved Doppler data, we explore the systematic trends in these parameters with disk position, as well as the effects that these parameters have on our estimation of the parameters of primary interest.