Unraveling Jupiter's Enigmatic Ionosphere from Galileo and Juno Radio Occultations

Radio occultation measurements from the Galileo, Voyager, and Pioneer missions have unveiled many mysteries in the Jovian ionosphere. The altitudinal structure of the Jovian ionosphere appears to be highly variable, although it is difficult to distinguish if the variability is spatial or temporal; and clear evidence of non-solar produced local time and latitudinal trends are observed. We present a quantitative analysis of all available sub-auroral radio occultation data, including new data from Juno, showing that the ionosphere’s vertical structure depends strongly on local time, longitude, and magnetic field geometry. Consequently, we investigate the key drivers of spatially variable plasma transport at non-auroral latitudes, namely: ambipolar diffusion, equatorial electrodynamics, and neutral wind-driven field-aligned flows. Our results indicate that neutral wind-driven field-aligned transport effectively organizes the observed electron density profiles, where model predictions of upward or downward plasma motion corresponds to higher (>1500 km) or lower (<1000 km) ionospheric peaks, respectively. This suggests that altitudinal structure of the non-auroral Jovian ionosphere may be temporally stable but spatially variable. However, highly variable ionospheric structure persists in the dusk ionosphere in regions where no plasma motion is predicted. The complexity of this variability will be discussed further in our presentation.