Meridional flow measurements of the Sun
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The meridional flow in the solar convection zone is a key ingredient of
some solar dynamo models. A poleward flow is observed at the surface
layers of the Sun. By mass conservation, this flow must eventually turn
equator-ward at a certain depth. At what depth this occurs, and with what
return velocities, and whether the vertical structure is single- or
multi-celled, are important but challenging questions for helioseismology.

In this seminar, I will give a short introduction to helioseismology,
discuss briefly the importance of the meridional flow in some theoretical
models (flux-transport dynamo models and mean-field models of angular
momentum transport), and then present our meridional flow observations
obtained with SOHO/MDI, which have the aim to measure the flow
profile with depth. First exciting results show for the first time a
possible return flow at a depth of around 40 Mm. We also find that the
radial flow profile changes with the 11-year solar cycle.