Juno Observations of Large‐Scale Azimuthal Fields and Flows in Jupiter's Nightside Magnetosphere: Field‐Aligned Currents, Effective Ionospheric Pedersen Conductivity, and Power to Atmospheric Heating

Abstract Using the methodology of Cowley et al. ( https://doi.org/10.1029/2025JA033993 ), we employ ∼8 years of Juno azimuthal magnetic field data to derive colatitude profiles of Jupiter's nightside (17‐05 hr via midnight) ionospheric equatorward Pedersen current from near the magnetic pole to inner magnetosphere field lines at 18° colatitude, from which we quantify large‐scale field‐aligned currents on spatial scales ∼1°. Polar‐tail Pedersen currents are ∼1–2 MA per radian of azimuth, with regions of downward and upward currents of order tens nA m −2 . Stronger downward currents ∼50–200 nA m −2 flow in an outer magnetosphere layer that is wider at dusk (∼7°) than at dawn (∼2°), with peak Pedersen currents near the outer/middle magnetosphere boundary reaching ∼12 MA rad −1 at dusk falling to ∼2.5 MA rad −1 at dawn. Upward currents of order hundreds of nA m −2 flow on middle magnetosphere field lines across which the Pedersen current falls to small values. The Pedersen currents are also combined with Juno/JADE‐I plasma angular velocity measurements to determine Jupiter's effective ionospheric height‐integrated Pedersen conductivity, together with the power input to thermospheric heating. Outer magnetosphere effective conductivities are ∼0.4 mho at dusk, falling to ∼0.25 mho at midnight, and ∼0.1 mho pre‐dawn. No significant increase in conductivity is found in the middle magnetosphere region of strong upward current, suggesting that thermospheric winds closely track the plasma velocity in this region. Latitude‐integrated powers show a similar dusk‐dawn asymmetry, with a total nightside power per hemisphere of ∼370 TW, of which ∼55% is input to thermospheric heating and 45% to the magnetospheric plasma.