Local Time Asymmetries in Jupiter's Magnetodisc Currents

C. T. S. Lorch,A. Bader,C. S. Arridge,C. J. Martin,L. C. Ray,K. K. Khurana

doi:10.1029/2019ja027455

Abstract

AbstractWe present an investigation into the currents within the Jovian magnetodisc using all available spacecraft magnetometer data up until 28 July 2018. Using automated data analysis processes as well as the most recent intrinsic field and current disk geometry models, a full local time coverage of the magnetodisc currents using 7,382 lobe traversals over 39 years is constructed. Our study demonstrates clear local time asymmetries in both the radial and azimuthal height‐integrated current densities throughout the current disk. Asymmetries persist within 30 R where most models assume axisymmetry. Inward radial currents are found in the previously unmapped dusk and noon sectors. Azimuthal currents are found to be weaker in the dayside magnetosphere than the nightside, in agreement with global magnetohydrodynamic simulations. The divergence of the azimuthal and radial currents indicates that downward field‐aligned currents exist within the outer dayside magnetosphere. The presence of azimuthal currents is shown to highly influence the location of the field‐aligned currents, which emphasizes the importance of the azimuthal currents in future magnetosphere‐ionosphere coupling models. Integrating the divergence of the height‐integrated current densities, we find that 1.87 MA R of return current density required for system closure is absent.

Highlights

The existence of a current disk at Jupiter has been well established since the flybys of the Pioneer probes in the 1970s
The radial and azimuthal Height Integrated Current Densities (HICDs) were calculated using the modal values for Bρ, Bφ and Bz in the lobe regions
The azimuthal HICDs are larger in the midnight through dawn sectors than in noon through dusk

Summary

Introduction

The existence of a current disk at Jupiter has been well established since the flybys of the Pioneer probes in the 1970s W. Hill & Michel, 1976; Smith et al, 1974). This current disk is a consequence of the strong rotationally driven dynamics that dominate the Jovian magnetosphere. Unlike at Earth where the current sheet is present only in the tail region, Jupiter’s current disk is present throughout all local times. A plasma disk is formed from plasma known to originate primarily from the volcanic moon Io, comprising of mostly atomic sulphur and oxygen dissociated from SO2. Iogenic neutrals are ejected into the local space environment and ionised. Lorentz forces accelerate the plasma towards corotation with the planet,

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