On the Penetration of Meridional Circulation below the Solar Convection Zone

Meridional flows with velocities of a few meters per second are observed in the uppermost regions of the solar convection zone. The amplitude and pattern of the flows deeper in the solar interior, in particular near the top of the radiative region, are of crucial importance to a wide range of solar magnetohydrodynamical processes. In this paper, we provide a systematic study of the penetration of large-scale meridional flows from the convection zone into the radiative zone. In particular, we study the effects of the assumed boundary conditions applied at the radiative-convective interface on the deeper flows. Using simplified analytical models in conjunction with more complete numerical methods, we show that penetration of the convectively driven meridional flows into the deeper interior is not necessarily limited to a shallow Ekman depth but can penetrate much deeper.