A Juno-era View of the Electric Currents in Jupiter's Magnetodisc

Abstract

Jupiter's main auroral emission is believed to be governed by a magnetosphere-ionosphere coupling current system resulting from the radial outflow of the iogenic plasma. To better understand, here we delineate this current system from the viewpoint of the magnetodisc, using Juno data obtained in the night-to-dawn magnetosphere during 2016-2020. We first derive a spatial distribution of the height-integrated radial (Ir) and azimuthal (Ia) currents in the magnetodisc. Then, we calculate the divergence of the two current components, which, according to current continuity, gives the field-aligned current (FAC) connecting the magnetodisc and the ionosphere. The Ir-associated FAC, Jr, flows into and out of the magnetodisc at small and large radial distances, respectively, approximately consistent with the axisymmetric corotation enforcement model. On the other hand, Ia decreases with increasing local time in the local time extent covered, indicating an additional FAC (Ja) flowing out of the magnetodisc. From Ia and Ja, we conclude that the influence of the solar wind, which compresses the dayside magnetosphere and thus breaks the axisymmetry, reaches deep to a radial distance of at least 20 Jupiter radii. Further efforts in modeling Jupiter's magnetosphere should take this factor into account.