In the recent papers, we introduced a method utilised to measure the flow field. The method is based on the tracking of supergranular structures.
We did not precisely know, whether its results represent the flow field in the photosphere or in some subphotospheric layers. In this paper, in combination with helioseismic data, we are able to estimate the depths in the solar convection envelope, where the detected large-scale flow field is well represented by the surface measurements.