Processes operating in the outer layers of the Sun’s atmosphere, the fully ionised, magnetically dominated plasma of the corona, remain one of the major unsolved puzzles in solar physics. Intensively debated research topics include the enigmatic problem of coronal heating; the rapid release of enormous amounts of magnetic energy in solar flares and coronal mass ejections; the microphysical mechanisms responsible for the efficient acceleration of charged particles; among others.

The solar physics community is strongly supported by a range of ground-based and spaceborne observational facilities, which provide a wealth of high-precision data across the entire electromagnetic spectrum, from radio waves to gamma-rays. Nevertheless, several key parameters of the solar corona, such as the magnetic field, the heating function, and the effective coefficients of thermal conduction, viscosity, and resistivity remain inaccessible to direct observation.

The method of magnetohydrodynamic (MHD) seismology, which infers plasma parameters from the properties of MHD waves, offers a paradigm-shifting diagnostic tool for probing the coronal plasma. Modern MHD seismology makes use of a range of MHD modes observed in different plasma structures to determine fundamental physical parameters of the corona and to diagnose the processes at work there.