Temporal cross-covariance computed with (Atmo Non Local) and (Dirichlet) boundary conditions, originating from the center, with frequencies selected around 3 mHz (left panel) and 6.5 mHz (right panel). As a comparison, we also plot the cross-covariance when using the (Reference) BC (dashed cyan line). The signal is multiplied by exp(t/ 90min) to counteract the effect of the damping, and normalized by the maximum of its amplitude at t = 30 min. The amplitude is plotted as a function of the acoustic depth for better readability of near-surface behavior. The dashed line indicates the solar surface.