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Properties of Near-surface Flows around Active Regions from Helioseismic Holography


Braun Douglas


NorthWest Research Assoc., CoRA DIvision


Local helioseismology
Auteur(s) supplémentaire(s)K. Wan


A variety of local-helioseismic analyses have reportedly shown large-scale ~50 m/s flows converging on active regions, although few quantitative and systematic studies have been made. We have examined the average properties of both the 75 strongest converging and 75 strongest diverging flows present in Carrington rotation CR1988, as identified from spatially-smeared maps of the horizontal divergence of flows within the uppermost 3 Mm of the Sun. The flows, averaged over 5 days, were deduced from calibrated helioseismic holography measurements applied to MDI observations of CR1988. We show that converging flows near active regions are common, but are significantly more compact than sometimes reported. Averaged over all azimuthal angles, inflows reach a peak speed of 40 m/s at about 35 Mm from their centers and fall to zero by a radius of 90 Mm (or 7 degrees). Similar converging flows, however, are also present in the quiet Sun, as are outflows with similar speeds and radial profiles near both active and quiet regions. It is speculated that the converging flows in active regions may represent normal components of solar convection (i.e. not necessarily requiring a different physical cause), but that AR magnetic fields provide a relatively long-lived boundary against which converging flows can persist and grow.

This work is supported by the Astronomical Sciences Division of the National Science Foundation (AST-0406225).
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