Flows in the Photosphere and in the Interior in Two Active Regions

Liu Yang yliu@sun.stanford.edu, Stanford University, United States
Zhao Junwei, Stanford University
Schuck Peter, NASA

Abstract
We study flows in the photosphere and at a layer 0.5 Mm below the photosphere (-0.5 Mm layer) in two solar active regions, AR 11084 on 2010 July 2 and AR 11158 on 2011 February 14. AR 11084 is a mature, simple active region that did not produce any flares during its disk passage. In contrast, AR 11158 is a multipolar, complex active region that was emerging on the date studied. It produced several major flares during its disk passage. Flow in the photosphere is derived by applying an inversion method, the Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM; Schuck 2008), to the time-series vector magnetic field data taken by the {\it Helioseismic and Magnetic Imager} (HMI) onboard the {\it Solar Dynamics Observatory} (SDO); flow at the -0.5 Mm layer is inferred by the time-distance helioseismology technique that is applied to the photospheric Doppler velocity measurements by HMI. AR 11084 shows very similar flow patterns in both layers: inward-flows in the sunspot umbra and outward-flows in the areas surrounding the sunspot. The boundary that separates the inward- and outward-flows is within the sunspot penumbra, which is different in the photosphere and at the -0.5 Mm layer. The inward-flow area in the sunspot is smaller in the photosphere than that at the -0.5 Mm layer. In other words, flows in some sunspot areas that have become outward-flow in the photosphere are still inward-flows at the -0.5 Mm layer. For the emerging, complex active region AR\,11158, flows in the two layers show great similarity in some areas and significant difference in other areas. On one hand, both layers display very consistent outward-flow in the areas surrounding sunspots; on the other hand, most well-documented flux-emergence-related flow features seen in the photosphere, such as strong shear motion along magnetic neutral line, fast spinning in sunspots, and separation motion between leading and following polarities during their dramatic emergence process, do not have their counterparts at the -0.5 Mm layer; Instead, it is exhibited evident inward flows in the sunspots at that layer. This implies that the horizontal flows caused by flux emergence are only in the atmosphere (e.g., the photosphere) but do not penetrate extensively into the interior.