Stream function of the estimated meridional flow of case 3 at the end of assimilation, with a latitudinal sampling restricted to (a) the northern hemisphere, (b) the southern hemisphere, and (c) the activity band. Observations are made every month for 1.5 solar cycles. This shows that observing in one hemisphere leaves the estimation of the meridional circulation in the other hemisphere less ideal. In (c), the synthetic observations are noised with ϵ = 1% (see text for details).