Description
Meridional Circulation (MC) in the Sun is an essential component in the solar dynamo mechanism. There have thus been a number of attempts to infer the solar internal MC profile via, e.g., time-distance helioseismology. We have however not reached an agreement even about the large-scale morphology of the internal MC profile. For example, whether the MC profile is overall single-cell or double-cell is not evident. This is partly due to the difficulty in inverting measured travel times in which the signal of the solar MC is small. In this talk, we present inversion results obtained with an additional constraint that the angular momentum (AM) transport by MC should be equatorward. Putting this physical constraint is motivated by a recent numerical result (Hotta and Kusano 2021, Nature Astronomy) where the solar equator-fast rotation is successfully reproduced without any tweaking. Inversion of the travel times measured by Gizon et al. (2020, Science) with this constraint results in a double-cell MC profile. Our result is compatible with a theoretical argument that the AM transport by single-cell MC is always poleward when we assume the mass conservation in the convective zone. However, we have also confirmed that the averaging kernels targeting around the deep convective zone are not well localized enough for us to conclude that the solar MC profile is double-cell. Although we have thus not reached a definitive conclusion on the large-scale morphology of the solar MC profile yet, our attempts highlight the relevance of investigating the solar MC profile from both theoretical and observational perspectives.
