Helioseismology and the solar interior dynamics

The inversion of helioseismic modes leads to the sound velocity inside the Sun with a precision of about 0.1 per cent. Comparisons of solar models wit h the "seismic sun" represent powerful tools to test the physics: depth of the convection zone, equation of state, opacities, element diffusion proces ses and mixing inside the radiative zone. We now have evidence that microsc opic diffusion (element segregation) does occur below the convection zone, leading to a mild helium depletion in the solar outer layers. Meanwhile thi s process must be slowed down by some macroscopic effect, presumably rotati on-induced mixing. The same mixing is also responsible for the observed lit hium depletion. On the other hand, the observations of beryllium and helium 3 impose specific constraints on the depth of this mildly mixed zone. Heli oseismology also gives information on the interval solar rotation: while di fferential rotation exists in the convection zone, solid rotation prevails in the radiative zone, and the transition layer (the so-called "tachocline" ) is very small. These effects are discussed, together with the astrophysic al constraints on the solar neutrino fluxes.