Solar Oscillations and the Magnetic Atmosphere

With the launch of the SOHO and TRACE satellites two new branches of solar physics have emerged: time-distance helioseismology and coronal seismology. In time-distance helioseismology the travel time of the acoustic waves between different points on the solar surface is measured to infer the local structure and properties of the subsurface layers of the Sun. The travel time changes due to the atmospheric magnetic field are evaluated theoretically. Coronal seismology utilises MHD waves in solar coronal structures as a tool to diagnose the physical parameters of the coronal plasma. Theoretical modelling of recently observed slow standing mode oscillations in stratified loops is presented. It is shown that large-amplitude resonant standing waves can be driven by small-amplitude oscillations at the chromospheric footpoints of the loops. The periods and the behaviour of these waves are different from those predicted by the classical theory of isothermal loop oscillations. The possible relationsheep between the oscillations studied in time-distance helioseismology and in coronal seismology is addressed.