Application of the Convected Kappa Distribution Function to Hot Plasma Ion Populations Observed in the Magnetospheres of Jupiter and Saturn

Abstract:

The Voyager, Galileo, and Cassini missions have measured the hot ion plasma pervading the magnetospheres of Jupiter and Saturn. In the middle and outer regions, the convected kappa distribution function, with isotropy in the rest (subcorotating with the planet) frame, has been found to fit hot ion particle distributions well and has been useful for extracting physical plasma parameters including the vector bulk velocity and the characteristic energy (temperature) of the distribution. The kappa model of the plasma distribution function using hydrogen and oxygen ions (Saturn) and hydrogen, oxygen, and sulfur ions (Jupiter) applied to observations generally indicates the presence of a hot ion population, energized in inner regions and adiabatically transported to the outer regions, but with significant exceptions. Higher mass species generally have a higher temperature. From the anisotropy of the distribution in the spacecraft frame, vector bulk velocity may be determined. From this analysis rotation curves for the plasma disks at Jupiter and Saturn reveal a plasma with significant subcorotation with a fraction that falls with increasing distance from the planet. There are local time asymmetries observed in the radial convection pattern. The plasma azimuthal convection patterns at Jupiter and Saturn and the characteristic temperature profiles are remarkably similar when scaled by the magnetopause distance and radial size of the planets.