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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 86, NO. A10, PAGES 8125–8140, 1981

Energetic Particle Events (≥30 keV) of Jovian Origin Observed by Voyager 1 and 2 in Interplanetary Space

R. D. Zwickl

University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico 87545.

S. M. Krimigis

Applied Physics Laboratory, The John Hopkins University, Laurel, Maryland 20810.

J. F Carbary

Applied Physics Laboratory, The John Hopkins University, Laurel, Maryland 20810.

E. P. Keath

Applied Physics Laboratory, The John Hopkins University, Laurel, Maryland 20810.

T. P. Armstrong

Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 60044.

D. C. Hamilton

Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742.

G. Gloeckler

Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742.

Abstract

Short-lived and long-lived ion flux increases (E ≥ 30 keV) of Jovian origin have been observed by the low energy charged particle (LECP) instrument on the Voyager 1 and 2 spacecraft. The short-lived events are observed more than 860 R_J upstream and more than 1500 R_J downstream of Jupiter. Observations of long-lived events appear to be confined to ≲200 R_J upstream of Jupiter. The short-lived events last from a few minutes to a couple of hours, while the long-lived events last from 8 to 21 hours. Both types of events have sharp onsets and decays, are usually confined to energies below 1 MeV total energy, and show a large general enrichment of Z ≥ 6 particles relative to proton and helium particles when compared with energetic particle events of solar or interplanetary origin. Many of the events have a noticeable peak in the energy spectrum above 100 keV after the main portion of the event. In addition, the short-lived events (upstream and downstream) are (1) extremely anisotropic with a flow direction consistent with flow away from Jupiter, (2) display no noticeable velocity dispersion, and (3) display initially steep energy spectra that flatten with time. The peak flux level at the lowest energies in the magnetosheath is similar to that observed during long-lived events. We conclude that a significant fraction of the particles observed during Jovian ion events originate from within the magnetosphere of Jupiter and simply leak out into the magnetosheath. If the interplanetary magnetic field favorably connects to the bow shock, particles can leak out into the interplanetary medium. Together with the necessary leakage model, the observations presented here cannot rule out the existence of a wave particle acceleration region located immediately upstream of the bow shock.

Received 25 June 1980; accepted 18 November 1980.

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Citation: Zwickl, R. D., S. M. Krimigis, J. F. Carbary, E. P. Keath, T. P. Armstrong, D. C. Hamilton, and G. Gloeckler (1981), Energetic Particle Events (≥30 keV) of Jovian Origin Observed by Voyager 1 and 2 in Interplanetary Space, J. Geophys. Res., 86(A10), 8125–8140.

Copyright 1981 by the American Geophysical Union.