Flows around the NOAA 11158 active region at various depths in the subphotospheric zone

This study analyzes velocity fields in the Sun’s convection zone at depths from 0.5 to 19 Mm at different evolutionary stages of active region NOAA 11158 (from 09 to 18 February 2011), obtained using techniques of time-distance helioseismology, within the general problem of investigating flow structural organization and dynamics. The data are supplemented with the photospheric velocity fields derived by means of local correlation tracking (LCT) and Doppler measurements. Since the helioseismological determinations of vertical velocities, Vz, are subject to very large errors due to the cross-talk effect, these velocities were also calculated from the divergence of horizontal velocities, divVxy, via the continuity equation in anelastic approximation. Annular structures, likely of convective nature, were detected in the velocity field at depths down to 6 Mm. We present the results of analysis of the correlation between vertical velocities and the divergence of horizontal flows. The dynamics of the correlation coefficient reveals three distinct stages in the evolution of the flow structure: a quiet state, flow formation, and steady fast flows. The correlation coefficient behaves differently at various depths during the quiet and active phases of the evolution. Furthermore, we detected a minimum in the correlation depth profile at ∼8.5 Mm during the quiet period. We conjecture that this feature is related to the supergranulation layer lower boundary, which is presumably located at such depths and reflects a change in the flow orderliness scale from supergranular to giant.