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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 103, NO. E9, PAGES 20,055–20,073, 1998

Energetic ion populations and periodicities near Jupiter

G. C. Anagnostopoulos

Department of Electrical and Computer Engineering, Demokritos University of Thrace, Xanthi, Greece


P. K. Marhavilas

Department of Electrical and Computer Engineering, Demokritos University of Thrace, Xanthi, Greece


E. T. Sarris

Department of Electrical and Computer Engineering, Demokritos University of Thrace, Xanthi, Greece


I. Karanikola

Department of Electrical and Computer Engineering, Demokritos University of Thrace, Xanthi, Greece


A. Balogh

Space and Atmospheric Physics Group, The Blacket Laboratory, Imperial College, London


Abstract

The HISCALE experiment, during Ulysses' approach to Jupiter, observed a ∼10 hour periodic softening in ion spectrum outside the plasma sheet that (1) is not related to the approach of the plasma sheet, (2) is in phase with the «clock» relativistic electron modulation, and (3) is related to flux increase at low energies (≤ 200 keV) and flux decrease at high energies (≥ 200 keV); the observations suggest the existence of an ion population with energy spectrum that is in general softer than the spectrum of the plasma sheet population. Detailed examination of the data shows that series of short duration (from a few up to some tens of minutes) energetic ion (∼0.06 to ∼3.00 MeV) bursts is a global phenomenon of the dayside Jovian magnetosphere and its environment. The bursts are often periodic at ∼40 min, although a second harmonic at ∼20 min is also evident in some cases. The energetic (≥∼60 keV) ion observations suggest that the plasma sheet was the main source of the upstream events inbound. The upstream observations (intensity-time profiles, energy spectra, velocity dispersion, angular distributions and composition) made by Ulysses (and earlier observations by Voyager missions, i.e. inverse velocity dispersion) are well explained in terms of magnetospheric periodicities (10 / 5 hours and 40 / 20 min) and a leakage model for magnetospheric ions. During the outbound trajectory, Ulysses detected a low energy (≤∼200 keV) ion population, that is discussed in terms of shock drift acceleration.

Received 22 August 1997; accepted 3 April 1998.

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Citation: Anagnostopoulos, G. C., P. K. Marhavilas, E. T. Sarris, I. Karanikola, and A. Balogh (1998), Energetic ion populations and periodicities near Jupiter, J. Geophys. Res., 103(E9), 20,055–20,073.