Energetic Charged-Particle Phenomena in the Jovian Magnetosphere: First Results from the Ulysses COSPIN Collaboration

Abstract

The Ulysses spacecraft made the first exploration of the region of Jupiter's magnetosphere at high Jovigraphic latitudes ( approximately 37 degrees south) on the dusk side and reached higher magnetic latitudes ( approximately 49 degrees north) on the day side than any previous mission to Jupiter. The cosmic and solar particle investigations (COSPIN) instrumentation achieved a remarkably well integrated set of observations of energetic charged particles in the energy ranges of approximately 1 to 170 megaelectron volts for electrons and 0.3 to 20 megaelectron volts for protons and heavier nuclei. The new findings include (i) an apparent polar cap region in the northern hemisphere in which energetic charged particles following Jovian magnetic field lines may have direct access to the interplanetary medium, (ii) high-energy electron bursts (rise times </= 1 minute and energies extending to > approximately 17 megaelectron volts) on the dusk side that are apparently associated with field-aligned currents and radio burst emissions, (iii) persistence of the global 10-hour relativistic electron "clock" phenomenon throughout Jupiter's magnetosphere, (iv) on the basis of charged-particle measurements, apparent dragging of magnetic field lines at large radii in the dusk sector toward the tail, and (v) consistent outflow of megaelectron volt electrons and large-scale departures from corotation for nucleons.

Magnetoinertial Oscillations of Jupiter’s Inner Radiation Belt

“…During the inbound, Ulysses was largely conÐned to the ecliptic and was less likely to register either north or south circumpolar relativistic electron bursts even if they had occurred. In this case, Ulysses must have missed most of these QP-40 electron bursts but a few (Simpson et al 1992 ;McKibben et al 1993). In contrast, during the outbound, Ulysses had access to higher southern jovigraphic latitudes (D30È40 S¡) and was thus able to detect series of QP-40 relativistic electron bursts coming from the south polar region.…”

“…Regarding the almost exclusive detection of QP-40 burst activities in the dusk side at high south jovigraphic latitudes during the outbound leg of Ulysses (Simpson et al 1992 ;Stone et al 1992 ;McKibben et al 1993 ;MacDowall et al 1993), we note the following.…”

“…If the basic scenario presented in this paper contains an element of truth, then the instrument onboard the Ulysses spacecraft may actually have sampled relativistic electrons of the IRB (Simpson et al 1992 ;McKibben et al 1993). One would anticipate to detect QP-40 brightness oscillations of Jovian decimetric synchrotron radio emissions from the IRB, especially upon the arrival of high-speed solar winds at the Jupiter or Jovian magnetosphere.…”

“…During one IRB oscillation cycle, when a sequence of electron bursts along the boundary zone sweeps across Ulysses lengthwise tangentially for a duration of a few minutes, the burst proÐle would be a sharp rise followed by a gradual fallo †. Occasionally, Ulysses may go across the IRB boundary zone widthwise such that recorded relativistic electron burst proÐles would appear spiky (Simpson et al 1992 ;McKibben et al 1993).…”

“…During the two-week encounter of Jovian magnetosphere by the Ulysses spacecraft in 1992 February, the cosmic and solar particle investigation (COSPIN) instrument onboard discovered series of relativistic electron bursts MeV) (E Z 9 from the south polar area in the dusk side with a quasi-periodicity of D40 minutes (Simpson et al 1992 ;. In close correlation, the uniÐed radio and plasma wave (URAP) experiment, also onboard the Ulysses spacecraft, recorded radio bursts (frequency kHz) with the same 40 minutes quasi-period (Stone l [ 700 et al 1992 ;MacDowall et al 1993 ;McKibben et al 1993).…”