A Statistical Analysis of the Returning Flux Tubes in the Jovian Magnetosphere Based on Juno Observations

Abstract The interchange process is an important mechanism for radial transport of plasma in the magnetospheres of the gas giants, namely Jupiter and Saturn. During this process, dense and cold flux tubes that move outwards are replaced by returning flux tubes with warm and tenuous plasma. In this study, we conduct a statistical analysis of the magnetic variation and plasma properties inside the returning flux tubes, based on the observations from magnetometer (MAG) and JADE onboard the Juno spacecraft during its first 45 perijove traverses. We detect the returning flux tubes by recognizing the low-energy electron flux sudden drop, within the range of M < 20 R J (Jupiter radii). The results have illustrated that the flux tubes with increased magnetic field account for the majority of the events. There is no significant relationship between the events with increased or decreased magnetic field and magnetic latitude, and both types of events are observed mostly near the equatorial plane, while events with depressed magnetic field are more frequently observed at larger distances from Jupiter with longer time duration (or larger flux tube volume). Furthermore, the crossover energy separating decreased low-energy electron flux and increased high-energy electron flux of the returning flux tubes is around several keV, depending on the type of magnetic field variation. These results provide great insight into the mass and magnetic flux transport in the inner Jovian magnetosphere.