  Using a 3D global solver of the linearized Euler equations, we model acoustic
oscillations over background velocity flow fields of single-cell meridional
circulation with deep and shallow return flows as well as double-cell
meridional circulation with strong and weak reversals. The velocities are
generated using a mean-field hydrodynamic and dynamo model -- moving through
the regimes with minimal parameter changes; counter-rotation near the base of
the tachocline is induced by sign inversion of the non-diffusive action of
turbulent Reynolds stresses ($\Lambda$-effect) due to the radial inhomogeneity
of the Coriolis number. By mimicking the stochastic excitation of resonant
modes in the convective interior, we simulate realization noise present in
solar observations. Using deep-focusing to analyze differences in travel-time
signatures between the four regimes, as well as comparing to solar
observations, we show that current helioseismology techniques may offer
important insights about the location and strength of the return flow, however,
that it may not currently be possible to definitively distinguish between
profiles of single-cell or double-cell meridional circulation.

Solar and Stellar Astrophysics