Ring-analysis flow measurements of sunspot outflows

Abstract

We present a local helioseismological analysis of the convective flows around sunspots. The flow deductions were obtained from MDI Dopplergrams using ring-analysis techniques to measure Doppler shifts induced in solar acoustic oscillations. A novel multi-scale 3-D inversion procedure was used to self-consistently combine all ring-analysis data taken from a mosaic of analysis tiles spanning the solar disk. The inversion is multi-scale because in addition to folding together information from tiles located at different positions on the solar surface, it is capable of incorporating tiles of different sizes, thus, enabling fine control of the horizontal resolution and the probing depth. The inversion is based on sensitivity kernels computed with the Born approximation. Our inversion results indicate that outflow observed at the surface surrounding sunspots persists to unexpectedly deep depths (~ 7 Mm). These outflows appear to have two components, being comprised of a superficial moat flow and a deeper outflow whose strength peaks around 5 Mm.