Radial and Vertical Structures of Plasma Disk in Jupiter's Middle Magnetosphere

Abstract

AbstractThe Juno mission flew through the plasma disk near the equator in Jupiter's magnetosphere frequently. We identify 274 plasma disk crossings of Juno between 10 and 40 RJ from PJ5 to PJ44. Using a forward modeling method that combines the JADE‐I time‐of‐flight and SPECIES data sets, we perform a survey of ion properties in the plasma disk. Ions are heated from 1.5 to 6 keV between 15 and 30 RJ. Density and temperature are locally anti‐correlated. Assumed to be related to centrifugal instabilities, cold, dense plasma are commonly observed near midnight. Plasma corotates around Jupiter and the rigid corotation breaks down outside 15–20 RJ. The plasma bulk velocity increases from the post‐dusk sector to the pre‐dawn sector featuring injection flows in the pre‐dawn sector, which is consistent with the Vasyliunas cycle. Strong outflows (>100 km/s) are commonly observed outside 20 RJ and the average radial velocity increases with radial distance. The ion abundance changes between 10 and 18 RJ and that might indicate plasma sources and/or sinks near Europa and Ganymede. The vertical distribution of ions is controlled by the balance between centrifugal, pressure gradient, and ambipolar electric field forces. An example near the M‐shell of 13.5 shows that average plasma temperature increases by a factor of 10 from the disk center to edge, because cold ions are more confined near the equator. Lighter ions with higher charge states have more mobility along the field line and have larger scale heights. The observations are compared with multi‐species diffusive equilibrium model.