  Helioseismic inferences of large-scale flows in the solar interior
necessitate accounting for the curvature of the Sun, both in interpreting
systematic trends introduced in measurements as well as the sensitivity kernel
that relates photospheric measurements to subsurface flow velocities.
Additionally the inverse problem that relates measurements to model parameters
needs to be well-posed to obtain accurate inferences, which necessitates a
sparse set of parameters. Further, the sensitivity functions need to be
computationally easy to evaluate. In this work we address these issues by
demonstrating that the sensitivity kernels for flow velocities may be computed
efficiently in a basis of vector spherical harmonics. We are also able to
account for line-of-sight projections in Doppler measurements, as well as
center-to-limb differences in line-formation heights. We show that given the
assumed spherical symmetry of the background model, it is often cheap to
simultaneously compute the kernels for pairs of observation points that are
related by a rotation. Such an approach is therefore particularly well-suited
to inverse problems for large-scale flows in the Sun, such as meridional
circulation.
