ALBERT

Description: We report on a set of clear and abrupt decreases in the high-frequency boundary of whistlerode emissions detected by Cassini at high latitudes (about 40) during the low-altitude proximal flybys f Saturn . These abrupt decreases or dropouts have start and stop locations that correspond to L shells at the dges of the A and B rings. Langmuir probe measurements can confirm, in some cases, that the abrupt decrease in the high-frequency whistler mode boundary is associated with a corresponding abrupt electron density dropout over evacuated field lines connected to the A and B rings. Wideband data also reveal electron plasma oscillations and whistler mode cutoffs consistent with a low-density plasma in the region. he observation of the electron density dropout along ring-connecting field lines suggests that strong ambipolar forces are operating, drawing cold ionospheric ions outward to fill the flux tubes. There is an analog with the refilling of flux tubes in the terrestrial plasmasphere. We suggest that the ring-connected electron density dropouts observed between 1.1 and 1.3 R(sub s) are connected to the low-density ring plasma cavity observed overtop the A and B rings during the 2004 Saturn orbital insertion pass.

Description: The relationship between electron energy flux and the characteristic energy of electron distributions in the main auroral loss cone bridges the gap between predictions made by theory and measurements just recently available from Juno. For decades such relationships have been inferred from remote sensing observations of the Jovian aurora, primarily from the Hubble Space Telescope, and also more recently from Hisaki. However, to infer these quantities, remote sensing techniques had to assume properties of the Jovian atmospheric structure - leading to uncertainties in their profile. Juno's arrival and subsequent auroral passes have allowed us to obtain these relationships unambiguously for the first time, when the spacecraft passes through the auroral acceleration region. Using Juno /Jupiter Energetic particle Detector Instrument (JEDI), an energetic particle instrument, we present these relationships for the 30-kiloelectronvolts to 1-megaelectronvolts electron population. Observations presented here show that the electron energy flux in the loss cone is a nonlinear function of the characteristic or mean electron energy and supports both the predictions from Knight (1973, https://doi.org/10.1016/0032-0633(73)90093-7) and magnetohydrodynamic turbulence acceleration theories (e.g., Saur et al., 2003, https://doi.org/10.1029/2002GL015761). Finally, we compare the in situ analyses of Juno with remote Hisaki observations and use them to help constrain Jupiter's atmospheric profile. We find a possible solution that provides the best agreement between these data sets is an atmospheric profile that more efficiently transports the hydrocarbons to higher altitudes. If this is correct, it supports the previously published idea (e.g., Parkinson et al., 2006, https://doi.org/10.1029/2005JE002539) that precipitating electrons increase the hydrocarbon eddy diffusion coefficients in the auroral regions.