High‐resolution energetic particle measurements at 6.6 RE, 2. High‐energy proton drift echoes

Drifting bunches of protons in the 0.14- to 1.0-MeV energy range have been observed with good energy resolution by the charged particle analyzer instruments on the 1976-059A and 1977-007A satellites in geostationary orbit. Well-defined flux peaks are observed corresponding to as many as six circuits of the earth by these proton bunches. Some 52 clear events have been recorded by the instrument on 76-059 in 8 months of data, and several cases have been observed by both spacecraft. In the twenty-five cases studied in detail, the proton bunches appear to be injected at locations near midnight. All injections are closely associated with substorm onsets, but fewer than 10% of all substorms have associated high energy proton drift echoes. After injection the magnetic field Structure at ∼6.6 RE often appears to be stable for 1–2 hours, as evidenced by the constant periods between the drift echoes. Observations made using the two spacecraft separated by ∼4 hours of local time show many events which fit a picture of very localized injection and Simple drift in a stable magnetospheric field. The majority of events observed, however, show a more complex behavior than the simple injection-drift picture would imply.