Galileo, as the first orbiting spacecraft in an outer planet's magnetosphere, provides the opportunity to study global energetic ion distributions in Jupiter's magnetosphere. We present directional anisotropies of energetic ion distributions measured by the Galileo Energetic Particles Detector (EPD). The EPD measurements of proton (80–1050 keV), oxygen (26–562 keV/nucleon), and sulfur (16–310 keV/nucleon) distributions cover a wide energy range. Spatially, the data set includes measurements from 6 to 142 Jovian radii (RJ) and covers all local times inside the Jovian magnetosphere. For each species a single detector head scans almost the entire sky (≈ 4π sr), producing the three‐dimensional angular distributions from which the anisotropies are derived. Consequently, the resulting anisotropy estimates are both global and robust. Such anisotropies, generally produced by convective flow, ion intensity gradients, and field‐aligned components, have long been used to estimate flow velocities and to locate spatial boundaries within magnetospheres. They can therefore provide vital information on magnetospheric circulation and dynamics. We find that the EPD measured anisotropies in the Jovian magnetosphere are dominated by a component in the corotational direction punctuated by episodic radial components, both inward and outward. Under the assumption that anisotropies are produced predominantly by convective flow, we derive flow velocities of protons, oxygen ions, and sulfur ions. The validity of that approach is supported by the fact that these three independently derived flow velocities agree, to a large extent, in this approximation. Thus, for the first time, we are able to derive the global flow pattern in a magnetosphere of an outer planet. In a comparison between the first‐order EPD flow velocities and those predicted by a magnetohydrodynamic (MHD) simulation of the Jovian magnetosphere, we find that qualitatively the directions appear similar, although no firm evidence of steady outflow of ions has been observed at distances covered by Galileo. A first rough comparison indicates that the measured first‐order flow velocities are higher by at least a factor of 1.5 than the MHD simulation results.

Ulysses observations at 2.5 AU of 38–315 keV electrons and 61–4752 keV ions during February‐April 1991 suggest in several ways that, during periods of sustained high solar activity, the inner heliosphere serves as a “reservoir” for low‐energy solar particles. Particle increases were not associated one‐to‐one with large X‐ray flares because of their poor magnetic connection, yet intensities in March‐April remained well above their February levels. The rise phase of the particle event associated with the great flare of 2245UT March 22 lasted most of two days, while throughout the one‐week decay phase, the lowest‐energy ion fluxes were nearly equal at Ulysses and Earth (IMP‐8).

Abstract. The first mass-discriminated, hot ion distribution moments (pressure, energy intensity) are determined for hot >50-keV ions in Jupiter's inner magnetosphere at the outer edge of Io's plasma torus by using the Galileo energetic particle detector (EPD) data. These hot plasmas were significantly depleted during the Galileo encounter in 1995 as compared with the Voyager epoch of 1979. The depletion of the hot ions is apparently caused by enhanced charge exchange losses of hot ions, perhaps associated with enhanced emissions of neutral gases from the volcanoes of Io. Such neutral gas enhancements could simultaneously explain increases, reported elsewhere, in the densities of the cooler Io torus plasmas. The hot plasma changes may explain why radial transport interchange turbulence has been observed by Galileo in the Io torus regions, whereas such turbulence was not apparent during the Voyager encounters in 1979. The hot ion depletion could also play a role in explaining the apparent differences between the Jovian auroral configuration observed in recent years by the Hubble space telescope and ground observers and the configuration observed by Voyager. This possibility is much less certain, however.

We present the results of a statistical study of 4 years (1972–1976) of IMP 7 and 8 observations at ∼40 RE of 50‐ to 200‐keV upstream ion events measured with the JHU/APL Energetic Particle Experiment (EPE). We find a monotonic increase in the probability of observing upstream particle events with a decrease in the angle (θBn) between the interplanetary magnetic field (IMF) and the local shock normal at the point where the IMF intersects the bow shock, independent of the length of time of bow shock connection (if it exceeds ∼10 min). We find roughly equal probability of observing an event above a given flux from any portion of the bow shock with the same value of θBn, a growth time of the 50‐ to 200‐keV events of ∼10 min, a maximum attainable flux of ∼2.5×104 (cm²s sr)−1, and a positive correlation between the probability of exceeding a given flux and the 3‐hour Kp index. The results imply that the local structure of the bow shock in the immediate vicinity of the field line connection is the dominant influence in the generation process of energetic upstream particle events and that wave‐particle interactions produce a self‐throttling mechanism that limits the maximum flux of ions escaping the upstream foreshock.

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