Helioseismology of sub-photospheric flows

Results of forward modelling of acoustic wave propagation in a realistic solar sub-photosphere with a steady horizontal flow are presented. The simulations are based on fully compressible ideal hydrodynamical modelling in a Cartesian grid. The initial model is characterised by solar density and pressure stratifications taken from standard solar Model S, adjusted to suppress convective instability. Acoustic waves are excited by a non-harmonic source located close to and right below the depth corresponding to the photosphere. A series of numerical experiments with coherent horizontal flows of various depths and speeds are carried out. The implemented flow field may mimick horizontal motions of plasma surrounding a sunspot (e.g. local analysis) or differential rotation (global analysis). The influence of steady state on the propagation of the sound waves through the solar interior is analyzed. Time-distance analysis is applied to compute the direct observational signatures of the background bulk motions on the travel times and phase shifts. This approach allows direct comparison with observational data.