Fig. 3

Magnetic gas cloud driving MHD shock as described by Fokker (1963) near the Sun (A) and by Gold (1962) in the interplanetary medium (B). The left picture (A) is based on the observation of type IV radio bursts caused by electrons trapped in stationary and moving magnetic structures. ‘IVdecam’ represents the type IV burst at decametric wavelengths. ‘IVmB’ denotes stationary type IV bursts due to electrons trapped in loops that are quasi-stationary. The solar gas from eruptions was thought to have a frozen in magnetic field that was described as a magnetic bottle. The MHD shock driven by the magnetic bottle is thought to be responsible for type II bursts. In B the shock standoff distance ‘a’ is determined by the radius of curvature of the magnetic bottle, the shock Mach number, and the adiabatic index. The shock thickness ‘d’ is for collisionless shocks