Auroral Field‐Aligned Current Signatures in Jupiter's Magnetosphere: Juno Magnetic Field Observations and Physical Modeling

Abstract

AbstractWe analyze magnetic data obtained during northern high‐altitude traversals of Jovian middle magnetosphere (MM) field lines during the first 10 inbound data‐taking passes of the Juno spacecraft for azimuthal field perturbations associated with magnetosphere‐ionosphere coupling currents. Full traversals across the MM region occur on all 10 passes at radial distances ∼7 to 16 RJ (T1 traversals), followed in four cases by reversed traversals (T2) at ∼4 to 7 RJ. Signatures of upward field‐aligned currents were observed in all cases, closely collocated with the statistical main auroral oval when mapped along field lines to the ionosphere. Two T1 sheets carry currents ∼10 MA per radian of azimuth in ionospheric colatitudinal layers ∼1.2°, closely comparable with the ∼8.5 MA rad−1 theoretical model value of Cowley et al. (2008, https://doi.org/10.5194/angeo-26-4051-2008). The other T1 sheets typically carry half this current ∼5.1 MA rad−1 in layers half the width ∼0.56°, thus with comparable current densities ∼425 nA m−2. The T2 currents are smaller ∼3.4 MA rad−1 with current densities ∼120 nA m−2, a difference that may relate to locations on opposite sides of the main oval as reflected in near‐contemporaneous ultraviolet observations, though ionospheric field strengths are not greatly different. Comparison with northern near‐periapsis currents observed inside ∼2 RJ on the same passes by Kotsiaros et al. (2019, https://doi.org/10.1038/s41550-019-0819-7) yields a cross‐correlation coefficient ∼0.7 with our T1 currents, though Kotsiaros et al.’s mean current value of ∼3.8 MA rad−1 is somewhat less than our overall mean T1 value ∼6.2 MA rad−1. The differences may have spatial, temporal, or methodological origins.