Subsurface Structures and Flow Fields of an Active Region Observed by Hinode

We analyze a solar active region observed by Hinode Ca II H line using the time-distance helioseismology technique, and derive the subsurface structure and flow fields of this active region. The basic subsurface wave speed structure is essentially the same as the previous results obtained from MDI observations. The subsurface flow structure is also similar to the previous results, but the downward flows are more resolved. Additionally, vertical mass circulations outside the sunspot are more clearly detected, although no mass conservation constraints are imposed in the inversion procedure. Near a light bridge area, hotter plasma is found beneath, and flows divergent from this area are observed. Inside the sunspot umbra and penumbra, some organized divergent flow cells of an intermediate size between granulation and supergranulation are also observed. These initial results demonstrate the potential and importance of high-resolution helioseismology of sunspots.