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

Abstract

A variety of local-helioseismic analyses have shown ~50 m/s flows converging on active regions (ARs). We have examined the average properties of both the 75 strongest converging and 75 strongest diverging flows present in Carrington rotation CR1988 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. Inflows associated with ARs typically have maximum speed of between 20 and 60 m/s at about 3 heliocentric degrees from their centers and fall to zero by a radius of 7 degrees. Similar converging flows, however, are prevalent in the quiet Sun. Outflows of similar spatial extent, but signficantly larger speeds, are present diverging from sunspots (i.e. the moat flows). Many of the converging flows in ARs appear to simply mark the boundaries of the moats while others converge on plage regions. In general, large ARs containing sunspots contain a complex mixture of both inflows and outflows which, aside from sunspot moats, also appear similar in property to convective components of the quiet Sun.