At the time of intense solar flares, various types of enhanced radio emission from the Sun have been observed. Using such techniques as the swept frequency technique first developed by Wild and his associates, these enhanced emissions have been classified into five types. Of particular interest to radio astronomy at metre wavelengths is the slow drift type II bursts. A comprehensive study of these bursts has been made by Roberts (1959). It is now supposed that at the start of a flare an explosion occurs in the lower regions of the solar atmosphere ejecting a column of gas which travels radially outward from the region of the flare. This column of gas is bounded by a shock front which moves forward relative to this gas. This shock front is assumed to excite plasma oscillations in the solar corona giving rise to type II radiation. Velocities of these shock fronts have been determined by various workers.
Velocities of Shock Fronts in Solar Corona Generating Type II Radio Bursts at Metre Wavelengths