ABSTRACT

Solar-terrestrial physics deals with the interaction between matter emitted from the Sun and the geospace environment. The region of interest extends from the Sun’s surface to the Earth’s ionosphere. In this region all matter is in the plasma state. Many of the processes occurring in the region are Magnetohydrodynamic processes. The Sun is a medium-sized star, consisting largely of hydrogen with a significant fraction of helium. To a first approximation, it can be regarded a plasma in gravitational and magnetohydrostatic equilibrium. It is heated from within by a fusion reaction. Energy is conducted outwards from the core through the conduction region. At about two-thirds of the radius, convection becomes the dominant process. The visible surface of the Sun is called the photosphere. Its position defines the solar radius. Visually, it has a changing granular structure as a consequence of the convection processes going on below it. It may be disturbed by violent phenomena occurring in active regions.