Occurrences of Pc 1 pulsations in the course of magnetospheric substorms

Frequency-time displays of geomagnetic pulsations recorded at Kiruna, Sweden, during the summer months of the years 1964 and 1965 revealed the appearance of Pc 1 pulsations in the 4-sec band with a pronounced maximum of occurrence in the daytime. Many of these events showed a repetitive structure with values of the repetition time and dispersion parameters that indicate a generation region on shells with L between 7 and 10. The Pc 1 pulsations were frequently accompanied by cosmic noise absorption (CNA) and X-ray enhancements; however, the onsets of the pulsations and of the CNA do not in general coincide. A systematic variation with time was observed for the time difference between the onsets of the pulsations and the absorption. At 06 LT the CNA started about 1.5 hr earlier than the pulsations, and at 16 LT the CNA started about 0.5 hr later. Furthermore, a series of events on the days after the ssc of August 16, 1965, showed Pc 1 pulsations starting at Kiruna approximately 0.5 hr after the onset of negative magnetic bays at College, Alaska. The observations can be explained by the assumption that energetic electrons and protons are injected into the outer radiation zone on the night side of the earth during a magnetospheric substorm and that these particles reach the day side by drift. If only magnetic gradient and curvature drift is considered, particles with energies near 100 kev on a shell with L ≈ 8 are required for a quantitative description of the observations.