Diagnostics of Plasma Dynamics and Magnetism Inside the Sun by Helioseismology

Helioseismology observations from space missions SOHO and Hinode have provided tremendous amount of new information about thermodynamic properties and dynamics of plasma in the solar interior. The helioseismic diagnostics are based on measuring oscillation frequencies and travel times of acoustic waves excited by turbulent convection in subsurface layers. These diagnostics give us new insights into basic physical processes inside the Sun, formation of magnetic structures in the solar plasma and mechanisms of solar and stellar activity. Recent helioseismology results reveal the deep structure of sunspots and associated plasma flows, and also complicated dynamics of emerging magnetic flux tubes and formation of active regions. In particular, the formation and stability of strong concentrations of magnetic field in sunspots is probably associated with converging flow patterns below the surface and the filamentary structure of magnetic fields in the turbulent solar plasma. Similar self-organization MHD processes are likely to happen in other astrophysical plasmas.