Large-scale horizontal flows in the solar photosphere. IV. On the vertical structure of large-scale horizontal flows

TL;DR

This study combines helioseismic data and surface measurements to determine that large-scale horizontal flows in the solar photosphere are representative of plasma motion down to approximately 10 Mm depth, with different structures tracked in magnetic and quiet regions.

Contribution

The paper introduces a method to estimate the vertical structure of large-scale flows in the solar photosphere using combined helioseismic and surface data, clarifying the nature of tracked structures.

Findings

Large-scale flows are represented by plasma motion down to ~10 Mm depth.

Supergranular structures are tracked in quiet Sun regions.

Magnetic field structures dominate in magnetic regions.

Abstract

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 sub-photospheric 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. We got a clear answer to question what kind of structures we track in full-disc Dopplergrams. It seems that in the quiet Sun regions the supergranular structures are tracked, while in the regions with the magnetic field the structures of the magnetic field are dominant. This observation seems obvious, because the nature of Doppler structures is different in the magnetic regions and in the quiet Sun. We show that the large-scale flow detected by our method represents the motion of plasma in layers down to ~10 Mm. The supergranules may therefore be treated as the objects carried by the underlying large-scale velocity field.