Energetic ion (>~50kev) and electron (>~40kev) bursts observed by ULYSSES near Jupiter

Abstract A careful analysis of data collected by the HISCALE experiment on board Ulysses suggests that the quasi-periodic (QP) modulation of several or tens of minutes in flux and/or anisotropy/spectral observations is an almost permanent characteristic of the energetic (>∼50 keV) ion population in the outer and the high latitude middle magnetosphere of Jupiter. In most cases a periodicity of ∼5–20 min is evident, although periodicities of ∼40 min and ∼80 min were also observed. The ∼40 min and ∼80 min periodicities were often accompanied by other harmonics, for instance ∼20 min and ∼40 min periodicities respectively, and were preferentially observed in the dusk magnetosphere. Observations of QP series of energetic ion and electron bursts in the dusk high latitude magnetosphere, as for instance, strong anisotropy, forward velocity dispersion and time delay between the ion and the electron onsets, are consistent with a periodic acceleration / injection of particles, in the form of field-aligned beams, originated from the low altitude environment of the planet (∼8 R J from the planet surface); the QP intensity gradients perpendicular to the field observed in the dusk middle magnetosphere are consistent with spatial structures of energetic particle sheets crossed by the spacecraft. The QP bursts of energetic particles are often accompanied by bursts of radio and aurora emissions and are possible sources of these Jovian phenomena.