Limits to Penetration of Meridional Circulation below the Solar Convection Zone

Abstract

We show that meridional circulation, such as that observed at the top of and in the solar convection zone (CZ) by direct doppler and helioseismic techniques, cannot penetrate significantly below the bottom (~0.7 Rsolar) of the overshoot layer at the bottom of the CZ. Therefore, solar dynamo models that rely on penetration as deep as to 0.6 Rsolar are ruled out. The analysis we carried out to reach this conclusion elucidates two boundary layers, one of which we have not seen applied to astrophysical problems before. This analysis should be relevant to understanding interfaces between convective and radiative zones in stellar interiors generally.