The Pedersen and Hall Conductances in the Jovian Polar Regions: New Maps based on a Broadband Electron Energy Distribution

TL;DR

The paper addresses how auroral broadband electron precipitation affects Jovian ionospheric conductances, focusing on the Pedersen and Hall components (ΣP and ΣH). It combines Juno JEDI and UVS data to constrain a kappa-based precipitating electron distribution and uses the TransPlanet 1D electron-transport model to derive H3+ and CH5+ densities, from which conductivities and altitude-integrated conductances are computed using measurements of the Jovian magnetic field. The key finding is that broadband (kappa) distributions yield higher and more spatially extensive conductances than mono-energetic ones, with the magnitude depending on mean energy and cross-sections; results differ from those inferred by corotation-enforcement theory, implying possible additional electron acceleration processes or FAC-limiting mechanisms. The study provides high-resolution conductance maps for multiple perijoves and highlights potential north-south asymmetries, offering new constraints for magnetosphere–ionosphere–thermosphere coupling at Jupiter.

Abstract

The ionospheric Pedersen and Hall conductances play an important role in understanding the exchanges of angular momentum, energy and matter between the magnetosphere and the ionosphere/thermosphere at Jupiter, modifying the composition and temperature of the planet. In the high latitude regions, these conductances are enhanced by the auroral electron precipitation. The effect of a broadband precipitating electron energy distribution, similar to the observed electron distributions through particle measurements, on the conductance values is investigated. The new values are compared to the ones obtained from previous studies, notably when considering a mono-energetic distribution. The broadband precipitating electron energy distribution is modeled by a kappa distribution, which is used as an input in an electron transport model that computes the density vertical profiles of ionospheric ions. The vertical profiles of the Pedersen and Hall conductivities are then evaluated assuming that the conductivities are mostly governed by the densities of H3+ and CH5+. Finally, the Pedersen and Hall conductances are computed by integrating the corresponding conductivities over altitude. The Pedersen and Hall conductances are globally higher when considering a broadband electron energy distribution rather than a mono-energetic distribution. In addition, the use of the direct outputs of an electron transport model rather than the analytical expression presented in Hiraki and Tao (2008) as well as a change in the electron collision cross-sections also have significant impacts on the conductance values. Comparison between our results and the ones deduced from the corotation enforcement theory suggests that either a physical mechanism limits the field-aligned currents or the auroral electrons precipitating in the atmosphere are also accelerated by processes not associated with the field-aligned currents.

Figures (24)

• Figure 1: Schematic representation of the different steps implemented to compute the Pedersen (P.) and Hall (H.) conductances. $\langle E \rangle$ and $F_e$ are the electron mean energy and energy flux, respectively, $\kappa$ is related to the high energy slope of the broadband electron energy distribution, $B$ is the magnetic field intensity and $\nu_{i,e}$ are the ion/electron collision frequency with the neutrals.
• Figure 2: Broadband energy distributions of electrons measured in the loss cone by JEDI for several PJs when Juno was magnetically connected to the ME region. The number flux values are actually median values over a PJ.
• Figure 3: Density and temperature profiles of the neutral atmosphere.
• Figure 4: (a) UV brightness map for PJ1 north. (b) UV brightness map for PJ1 north after we applied a mask that hides the regions poleward and equatorward of the ME. On each map, the red star represents the subsolar longitude.
• Figure 5: Vertical profiles of (a)-(d) the densities of $\ce{H3+}$ and $\ce{CH5+}$, (e)-(h) the Pedersen conductivity and (i)-(l) the Hall conductivity, computed assuming either a kappa or a mono-energetic electron energy distribution and for $\langle E \rangle$ = 10, 30, 100 and 500 keV. The electron total energy flux is 1 mW.m-2.