Probing the Sun's Near Surface Shear Layer using HMI Spherical Harmonic Coefficients

We have measured zonal and meridional components of subsurface flows up to a depth of 30 Mm below the solar surface by applying the technique of ring diagram on Dopplergrams which are constructed from the spherical harmonic (SH) coefficients. The SH coefficients are obtained from the Helioseismic and Magnetic Imager (HMI) full-disk Dopplergrams. We find a good agreement and some differences between the flows obtained in this study with those from the traditional methods using direct Dopplergrams.