Modeling Jupiter's Dawnside Magnetodisc: Using Juno Observations to Constrain a Radial Force-Balance Model

Abstract

This study investigates Jupiter's dawnside magnetodisc, using plasma and magnetic field measurements from Juno orbits 5 to 12 to refine a radial force-balance magnetodisc model. This iterative vector potential model examines variations in the azimuthal magnetodisc current, coupled with a magnetosphere-ionosphere coupling model from which the radial current is simultaneously obtained. Three key force-balance parameters are used: the hot plasma parameter (pV, Pa m T⁻¹), the mass outflow rate of cold iogenic plasma, and the height-integrated ionospheric Pedersen conductivity. Axisymmetric equilibrium outputs are compared to Juno's residual magnetic field and heavy ion density data between 15 and 60 R_J. Optimal parameter values for each orbit and overall current distributions are determined. Averaged modeled values are (1.63 ± 0.17) × 10⁷ Pa m T⁻¹ for the hot plasma parameter, 1,340 ± 350 kg s⁻¹ for the mass outflow rate, and 0.26 ± 0.08 mho for the Pedersen conductivity. The overall modeled magnetodisc azimuthal current to 60 R_J is 266 ± 23 MA, varying similarly to the currents determined by Connerney et al. (2020, https://doi.org/10.1029/2020JA028138) but typically ∼50 MA larger. Of this total, the hot plasma current 158 ± 13 MA is larger than the cold plasma current 109 ± 23 MA, and dominates in the inner region. The cold plasma current typically becomes the larger component beyond ∼35 R_J and exhibits greater orbit-to-orbit variability. The mass outflow rate from Io is the primary driver of magnetodisc current variability. The north-south summed radial magnetosphere-ionosphere coupling current 104 ± 31 MA is typically ∼40% of the total azimuthal current, with variations that are only weakly correlated.