Interplanetary Shock

A shock wave is the interface separating an upstream flow from a downstream flow. It may be driven by a supersonic object (a piston) or it may be initiated by an "explosion". In the case of the shock shown in the Figure, occurring at approximately 12:40, the density and the magnetic field amplitude both increase downstream of the shock. The increase in density causes a corresponding increase in the plasma frequency, which may be seen in the behavior of the quasithermal noise.