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

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Title: Juno Observations of Large‐Scale Azimuthal Fields in Jupiter's Nightside Magnetosphere and Related Radial Currents.
Authors: Provan, G.1 (AUTHOR) gp31@leicester.ac.uk, Cowley, S. W. H.1 (AUTHOR), Nichols, J. D.1 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Oct2024, Vol. 129 Issue 10, p1-30. 30p.
Subject Terms: Juno (Space probe), Current sheets, Magnetosphere, Data binning, Jupiter (Planet)
Abstract: 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 ρ from the magnetic axis over 4–32 RJ along empirical poloidal model field lines spanning from tail to middle magnetosphere regions (ionospheric colatitudes θi ∼ 5°–17°), and by local time (LT). The data are well organized by these parameters. On southern tail field lines (∼5°<θi≤11° ${\sim 5{}^{\circ}< \theta }_{i}\le 11{}^{\circ}$) the azimuthal field is well represented as the sum of sweepback fields falling as 1/ρ that are near‐independent of θi and LT, and a near‐constant field consistent with ∼3.5 nT pointing sunward. The combination is swept back at dawn/midnight but swept forward at dusk outside ∼5 RJ. Outer magnetosphere (θi ∼ 12°–15.5°) 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/ρ field is associated with a nightside inward polar axial current ∼5.8 MA located within θi ∼ 5° of the magnetic axis, while the dusk‐midnight field shear measured near the ∼30 RJ study boundary provides an inward current ∼15.4 MA, related to the near‐constant field. Azimuthal fields fall to small values across middle magnetosphere field lines (θi ∼ 15.5°–17°), associated with outward currents ∼21.2 MA per hemisphere near‐independent of LT forming the nightside equatorial current sheet, balancing these inward currents. Key Points: We combine magnetic data from 46 Juno periapsides using a poloidal field model to examine Jupiter's nightside azimuthal fields to 32 RJOuter magnetosphere region fields at ∼30 RJ are swept back independent of LT associated with outward radial equatorial currents ∼13 MA rad−1Tail region fields are swept‐back at dawn/midnight but swept forward at dusk implying strong tail boundary inward currents ∼10 MA rad−1 [ABSTRACT FROM AUTHOR]
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Abstract: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 ρ from the magnetic axis over 4–32 RJ along empirical poloidal model field lines spanning from tail to middle magnetosphere regions (ionospheric colatitudes θi ∼ 5°–17°), and by local time (LT). The data are well organized by these parameters. On southern tail field lines (∼5°<θi≤11° ${\sim 5{}^{\circ}< \theta }_{i}\le 11{}^{\circ}$) the azimuthal field is well represented as the sum of sweepback fields falling as 1/ρ that are near‐independent of θi and LT, and a near‐constant field consistent with ∼3.5 nT pointing sunward. The combination is swept back at dawn/midnight but swept forward at dusk outside ∼5 RJ. Outer magnetosphere (θi ∼ 12°–15.5°) 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/ρ field is associated with a nightside inward polar axial current ∼5.8 MA located within θi ∼ 5° of the magnetic axis, while the dusk‐midnight field shear measured near the ∼30 RJ study boundary provides an inward current ∼15.4 MA, related to the near‐constant field. Azimuthal fields fall to small values across middle magnetosphere field lines (θi ∼ 15.5°–17°), associated with outward currents ∼21.2 MA per hemisphere near‐independent of LT forming the nightside equatorial current sheet, balancing these inward currents. Key Points: We combine magnetic data from 46 Juno periapsides using a poloidal field model to examine Jupiter's nightside azimuthal fields to 32 RJOuter magnetosphere region fields at ∼30 RJ are swept back independent of LT associated with outward radial equatorial currents ∼13 MA rad−1Tail region fields are swept‐back at dawn/midnight but swept forward at dusk implying strong tail boundary inward currents ∼10 MA rad−1 [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2024JA032677