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We derive horizontal fluid motions on the solar surface over large areascovering the quiet-Sun magnetic network from local correlation tracking ofconvective granules imaged in continuum intensity and Doppler velocity by theHelioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory(SDO). From these we calculate horizontal divergence, vertical component ofvorticity, and kinetic helicity of fluid motions. We study the correlationsbetween fluid divergence and vorticity, and that between vorticity (kinetichelicity) and magnetic field. We find that the vorticity (kinetic helicity)around small-scale fields exhibits a hemispherical pattern (in sign) similar tothat followed by the magnetic helicity of large-scale active regions(containing sunspots). We identify this pattern to be a result of the Coriolisforce acting on supergranular-scale flows (both the outflows and inflows), andis consistent with earlier studies using local helioseismology. Further, weshow that the magnetic fields cause transfer of vorticity from supergranularinflow regions to outflow regions, and that they tend to suppress the vorticalmotions around them when magnetic flux densities exceed about 300 G (HMI). Wealso show that such action of magnetic fields leads to marked changes in thecorrelations between fluid divergence and vorticity. These results arespeculated to be of importance to local dynamo action if present, and to thedynamical evolution of magnetic helicity at the small-scale.

Relationships between fluid vorticity, kinetic helicity and magnetic field at the small-scale (quiet-network) on the Sun