Development of shocks waves in the solar corona and the interplanetary space

At the Sun shock waves are produced either by flares or by coronal mass ejections and are regarded to be the source of solar energetic particle events. The propagation of a disturbance away from an active region through the corona into the interplanetary space is considered by evaluating the radial behaviour of the Alfven speed. The magnetic field of an active region is modelled by a magnetic dipole superimposed on that of the quiet Sun. Such a magnetic field structure leads to a local mimimum of the Alfven speed in the middle of the corona and a maximum of 740 km/s at a radial distance of 6 solar radii from the center of the Sun. The occurrence of these extrema of the Alfven speed has consequences for the formation and development of shock waves in the corona and interplanetary space.