Acoustic Wave Propagation in the Sun: Implications for Wave Field and Time-Distance Helioseismology

We present results of the numerical simulation of acoustic wave propagation in the Sunʹs subphotospheric layers. A finitedifference code is used to calculate the pressure perturbation in the frequency domain. We show that the oscillatory seismic signals are closely associated with the solar density and sound speed structures. Owing to the acoustic cutoff frequency, the reduction in the group velocity relative to the background sound speed varies significantly with frequency, especially at low frequencies. This variation causes acoustic wave dispersion, which results in the nonuniform frequency content in the oscillatory signals in the wave packets. An asymptotic arrival generated by the constructive interference of the high-order bounces is observed in the synthetic seismic traces. The synthetic seismic traces presented in this study can provide the basis for wave field tomography, in which phase and amplitude information (including the nonresonant frequencies) is exploited, to enhance the spatial resolution of the reconstructed solar models.