Local Time Asymmetries in Jupiter's Magnetodisc Currents

Abstract

We 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 normalJ 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 normalJ−2 of return current density required for system closure is absent.

Six Pieces of Evidence Against the Corotation Enforcement Theory to Explain the Main Aurora at Jupiter

“…Analyzing the equatorial magnetic field measurements of the whole Galileo mission, Lorch et al. (2020) also concluded that azimuthal currents play a key role in determining the location of the field‐aligned currents. Furthermore, Vogt et al.…”

“…It would consistently strengthen the total net field-aligned currents on the duskside and weaken the currents on the dawnside. Analyzing the equatorial magnetic field measurements of the whole Galileo mission, Lorch et al (2020) also concluded that azimuthal currents play a key role in determining the location of the field-aligned currents. Furthermore, Vogt et al (2019) noted that the dawn-dusk discrepancy on the bend-back angle is even larger during solar wind compressions, which should lead to a brightening of the dawn arc of the MEs but a dimming of the dusk arc if the corotation enforcement current were driving the main auroral emissions.…”

A Modular Model of Jupiter's Magnetospheric Magnetic Field Based on Juno Data

“…In the previous models, the current sheet is always assumed as a symmetric azimuthal (dawn-to-dusk direction) configuration while the current density decreases with the distance from the planet. However, from a detailed analysis by Lorch et al (2020), the current density varies with local time and the radial current should also be considered. So we employ the TS07 method (Tsyganenko & Sitnov, 2007) to construct the complex morphologies of the equatorial current system.…”

“…However, from a detailed analysis by Lorch et al. (2020), the current density varies with local time and the radial current should also be considered. So we employ the TS07 method (Tsyganenko & Sitnov, 2007) to construct the complex morphologies of the equatorial current system.…”

“…Besides the model of Khurana (1997), all other models are based on an assumption that the equatorial current is symmetric along the azimuthal direction and could not describe the sweep‐back nature of Jupiter's magnetic field. However, the structure of the current disk is complex and time‐dependent, including asymmetries of current density and thickness of the current sheet (Khurana & Schwarzl, 2005; Lorch et al., 2020). These complex asymmetries arise from both internal rotational stresses and external solar wind forcing on the system (Arridge et al., 2015).…”