Natural Sciences (Astrophysics and Astrononmy)
Although the principles involved in understanding ring-diagram mode frequencies are well understood, the procedures for determining those frequencies in the power spectra of flattened geometries are plagued by several systematic effects which are not well understood. It is possible to overcome these effects in certain cases by comparing inversions of the fitted mode parameters, or just the parameters themselves, for particular targets with those for otherwise similar targets. We can thus draw useful information about features localized in both space and time, such as regions of anomalous flows or the thermal structures of active regions. But reliable measurements of the large-scale or long-term mean dynamical structure of the near-surface regions, particularly the profiles of differential rotation and meridional circulation, may require more robust estimations of the mode parameters than are presently available. We describe the known systematic effects in the extensive ring-diagram analysis of HMI Doppler data and explore some methods of overcoming or dealing with them.
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