Evidence for confinement of low-energy cosmic rays ahead of interplanetary shock waves

Short-lived ( 15 min), low-energy proton increases associated with the passage of interplanetary shock waves have been previously reported. In the present paper, we have examined in a fine time scale ( 1 min) the concurrent particle and magnetic field data, taken by detectors on Explorer 34, for four of these events which occurred on 30 May 1967, 5 June 1967, 29 November 1967, and 11 January 1968. Our results further support the view that these impulsive events are due to confinement of the solar cosmic-ray particles in the region just ahead ( 10⁶ km) of the advancing shock front. Data from the Pioneer 7 spacecraft for a similar event on 30 August 1966, when this spacecraft was 1.9 × 10⁶ km from the Earth, are shown to be consistent with this interpretation.