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Keywords:

  • Sun;
  • ocal helioseismology;
  • sub-photospheric layers;
  • horizontal velocity field

Abstract

The dense-pack grid is commonly used to get a synoptic view of the sub-photospheric dynamics when using ring diagram analysis (Haber et al 2002). This grid is based on a fixed distribution of patches in central meridian distance (cmd) at all latitudes. A shortcoming of the dense-pack grid is that the true motion of tracked areas at slower rotating latitudes is not handled correctly. For instance, a 15° × 15° area, centered at a cmd of 0° and a latitude of 60°, that rotates only 12° in 1664 minutes (ring day), is considered tobe centered at cmd = 15° in the subsequent ring day. In order to avoid this issue, another distribution is suggested where the grid point in central meridian distance is latitude dependant (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)