Juno Observations of Large-Scale Azimuthal Fields in Jupiter's Nightside Magnetosphere and Related Radial Currents

We combine magnetic data from the first 46 data-taking periapsides of the polar orbiting Juno spacecraft spanning dawn to dusk via midnight to investigate azimuthal fields and related currents in Jupiter's nightside magnetosphere. Data are binned by perpendicular radial distance rho from the magnetic axis over 4-32 R-J along empirical poloidal model field lines spanning from tail to middle magnetosphere regions (ionospheric colatitudes theta(i) similar to 5 degrees-17 degrees), and by local time (LT). The data are well organized by these parameters. On southern tail field lines (similar to 5 degrees< theta(i )<= 11 degrees) the azimuthal field is well represented as the sum of sweepback fields falling as 1/rho that are near-independent of theta(i) and LT, and a near-constant field consistent with similar to 3.5 nT pointing sunward. The combination is swept back at dawn/midnight but swept forward at dusk outside similar to 5 R-J. Outer magnetosphere (theta(i) similar to 12 degrees-15.5 degrees) azimuthal fields are instead swept back near-independent of LT, near-continuous with the tail field in the dawn sector, but with large shear at the tail interface and across outer magnetosphere field lines in the dusk-midnight sector. The tail region 1/rho field is associated with a nightside inward polar axial current similar to 5.8 MA located within theta(i) similar to 5 degrees of the magnetic axis, while the dusk-midnight field shear measured near the similar to 30 R-J study boundary provides an inward current similar to 15.4 MA, related to the near-constant field. Azimuthal fields fall to small values across middle magnetosphere field lines (theta(i) similar to 15.5 degrees-17 degrees), associated with outward currents similar to 21.2 MA per hemisphere near-independent of LT forming the nightside equatorial current sheet, balancing these inward currents.