Probing plasma structures and dynamics inside the sun

Helioseismology has provided tremendous amount of new information about the thermodynamic properties and dynamics of plasma in the Sun's interior. This gives us new insights into the basic physical processes inside the Sun, formation of magnetic structures in the solar plasma and mechanisms of solar and stellar activity. In particular, the new results have revealed the deep structure of sunspots and associated complicated patterns of plasma flows, the dynamics of the emerging magnetic flux and formation of active regions, the supergranular structure and dynamics of the upper convection zone, as well as the global structures and circulation patterns in the deep interior, evolving with the activity cycle. In addition, first attempts are made to find links between the internal dynamics and processes of magnetic energy release in the solar corona. Understanding of these results, often puzzling and counter-intuitive, represents a major challenge for MHD theories of astrophysical plasma.