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Accurate inference of solar meridional flow is of crucial importance for theunderstanding of solar dynamo process. Wave travel times, as measured on thesurface, will change if the waves encounter perturbations e.g. in the soundspeed or flows, as they propagate through the solar interior. Using functionscalled sensitivity kernels, we may image the underlying anomalies that causemeasured shifts in travel times. The inference of large-scale structures e.gmeridional circulation requires computing sensitivity kernels in sphericalgeometry. Mandal et al. (2017) have computed such spherical kernels in thelimit of the first-Born approximation. In this work, we perform an inversionfor meridional circulation using travel-time measurements obtained from 6 yearsof SDO/HMI data and those sensitivity kernels. We enforce mass conservation byinverting for a stream function. The number of free parameters is reduced byprojecting the solution on to cubic B-splines in radius and derivatives of theLegendre-polynomial basis in latitude, thereby improving the condition numberof the inverse problem. We validate our approach for synthetic observationsbefore performing the actual inversion. The inversion suggests a single-cellprofile with the return-flow occurring at depths below 0.78 $R_\odot$.

Helioseismic inversion to infer depth profile of solar meridional flow using spherical Born kernels