Magnetohydrodynamic Waves and Seismology of the Solar Atmosphere

Abstract

The solar atmosphere is a gigantic plasma physics laboratory that has attracted attention from plasma physicists for over a century. It extends from the visible surface of the Sun or photosphere, into the corona and solar wind all the way to the Earth and beyond. The plasma of the solar atmosphere has properties that makes it a real challenge to study and fully understand. It is structured, inhomogeneous, highly dynamic and is characterized by a large range of spatial and temporal scales. Among the many unsolved questions of modern solar plasma physics a few emerge with importance well beyond the boundaries of solar physics. How is plasma in the corona heated to multi-million K temperatures? What are the fundamental underlying physical processes of plasma acceleration and solar wind generation? What are the physical processes that drive Space Weather? It has been predicted for several decades that magnetohydrodynamic (MHD) waves may play a key role in processes that determine the physical conditions in the solar atmosphere. However, due to the lack of adequate instrumental resolution there was only limited or indirect evidence for the existence of MHD waves. The actual discovery of magnetic or magnetically dominated waves with imaging and spectro-polarimetric instrumentation onboard of solar satellites supplemented with high-resolution ground-based instrumentation since the mid-1990s and into the new milenium has shed new light on MHD waves. Slow and fast magneto-acoustic waves and Alfven waves, predicted by theory, have now been observed in a wide variety of magnetic structures in the solar atmosphere. Research on MHD waves has evolved over the last two decades from a largely theoretical enterprise with little observational underpinning into a subject that is now driven by a wealth of observations which show that MHD waves are almost everywhere in the solar atmosphere. New theoretical developments are needed to understand and exploit the available observations. MHD waves