Impulsive precipitation events during an auroral breakup

It is now well established that large fluxes (109 cm−2 sec−1 ster−1) of low-energy (1–10 kev) protons are precipitated together with comparable electron fluxes during the breakup and post-breakup phases of the aurora [Bernstein et al., 1969a; Reasoner et al., 1968]. Although rapid variations in the electron precipitation have been reported [Evans, 1967; Lampton, 1967], to date the observational evidence indicates that the proton precipitation is relatively steady and is uniformly distributed over large spatial regions [Eather, 1967]. In this preliminary note, we wish to report qualitatively some rocket observations of abrupt impulsive increases in the precipitated 0.3- to 10-kev proton flux; the proton increases are associated with apparently equally abrupt decreases in the precipitated 0.2- to 6-kev electron flux. On April 17, 1969, at 00h 57m 30s local time (06h 57m 30s UT), the Nike-Tomahawk rocket was launched from Fort Churchill into an active coronal rayed form some 3 min after the magnetic field had reached a maximum depression of 150 γ. At the time of launch the breakup had begun, and by the end of the flight, ∼6 min later, the aurora was much diminished. The peak 5577-A intensity observed from the ground during the flight was ∼14 kR. There was ≤l-db 30-MHz riometer absorption in the event. A PCA event occurred some 5½ days before this flight, and possibly a second event occurred 4 days before the flight. On the day of the flight there was only a very slight indication of the PCA, and it is felt that the data reported below were not influenced by any solar cosmic rays.