Probing plasma properties and dynamics inside the Sun

Helioseismology experiment MDI on board the SOHO spacecraft has provided tremendous amount of new information about the thermodynamic properties and dynamics of plasma in the Sun's interior, uncovering remarkable new perspectives for studying complex interactions between turbulent convection, rotation and magnetism below the solar surface, and their relationship to solar irradiance variations and coronal 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 the links between the internal dynamics and processes of magnetic energy release in the solar corona. Understanding these results, often puzzling and counter-intuitive, is a major challenge for MHD theories of astrophysical plasma.