Moat flow system around sunspots in shallow subsurface layers

TL;DR

This study compares the subsurface moat flow system around sunspots with supergranular flows, revealing asymmetries and differences in flow direction and mass circulation rates through helioseismic analysis.

Contribution

It provides a detailed comparison of moat flows around sunspots and supergranular flows, highlighting key differences in symmetry, flow direction, and mass downflow rates.

Findings

Moat flows replace supergranular flows around sunspots.

Moat flows are asymmetrical, likely due to sunspot motion.

Mass downflow rate in moat is at least twice that of supergranules.

Abstract

We investigate subsurface moat flow system around symmetrical sunspots of McIntosh type H and compare it to the flow system within supergranular cells. Representatives of both types of flows are constructed by means of statistical averaging of flow maps obtained by time--distance helioseismic inversions. We find that moat flows around H-type sunspots replace the supergranular flows but there are two principal differences between the two phenomena: The moat flow is asymmetrical, probably due to proper motion of sunspots with respect to the local frame of rest, while the flow in the supergranular cell is highly symmetrical. Further, the whole moat is a downflow region, while the supergranule contains the upflow in the centre, which turns into the downflow at some 60 % of the cell radius from its centre. We estimate that the mass downflow rate in the moat region is at least two times larger than the mass circulation rate within the supergranular cell.