Investigation of mass flows beneath a sunspot by time-distance helioseismology

A time-distance helioseismic technique is employed to analyze a set of high -resolution Dopplergram observations of a large sunspot by SOHO/MDI on 1998 June 18. A regularized, damped least-squares inversion is applied to the m easurements of travel times to infer mass flows around the sunspot below th e solar surface. Powerful converging and downward directed flows are detect ed at depths of 1.5-5 Mm, which may provide observational evidence for the downdrafts and vortex flows that were suggested by Parker for a cluster mod el of sunspots. Strong outflows extending more than 30 Mm are found below t he downward and converging flows. It is suggested that the sunspot might be a relatively shallow phenomenon, with a depth of 5-6 Mm, as defined by its thermal and hydrodynamic properties. A strong mass flow across the sunspot is found at depths of 9-12 Mm, which may provide more evidence in support of the cluster model, as opposed to the monolithic sunspot model. We sugges t that a new magnetic emergence that was found 5 hr after our analysis peri od is related to this mass flow.