The supergranule velocity field

A study of supergranule motions confirms horizontal velocities with peak values of typically 0.36 km s-1 as observed in Fe I 8688 Angstroem. These show no significant variation with height over the range of formation of C I 9111, Fe I 8688, and Mg I 8806, but there is a substantial reduction to about one-half of this at the level of Ca II 8542. Near disk center, supergranule vertical velocites in Fe I 8688 have rms values <= +- 0.01 km s-1, after allowance for the residual effects of the line-of-sight component of the horizontal supergranule motions, the five-minute oscillations, granule motions, and detector drift. There is a marginally-significant association of magnetic elements, and hence of cell boundaries, with downward motions; but this requires further testing. Measurements of downward velocities >= 0.1 km s-1 in regions of strong magnetic field when using unpolarized light are attributed to the much higher downflow inside the elements themselves and have nothing to do with supergranule motions. (orig.)