A large proton event associated with solar filament activity

The authors report observations, made from several interplanetary spacecraft, of the large, low-energy particle event of April 23-27, 1979, associated with solar filament activity. The intensity and the spectral and directional evolution of the event as observed in the energy range 35-1600 keV on ISEE-3, located similar to 0.99 AU from the Sun upstream of the Earth, are discussed. It is demonstrated that the shock disturbance propagating through the interplanetary medium and observed at ISEE-3 on April 24-25 strongly controls the particle event. From a comparison of the ISEE-3 observations with those on other spacecraft, in particular on Helios-2, located at 0.41 AU heliocentric distance near the Sun-Earth line, the authors identify the solar filament erupting on late April 22 near central meridian as the trigger for the propagating shock disturbance. This disturbance, a forward shock and a reverse shock at the orbit of ISEE-3, is found to be the main source of the energetic proton population observed.