A model for the secular magnetic field variation caused by Jupiter’s zonal winds

Abstract

<p>The secular variation of the geomagnetic field is routinely used to infer the flow on the top of Earth’s liquid iron core. Recent gravity measurements by the Juno spacecraft suggest that the zonal winds observed on Jupiter’s surface reach about 3000 km deep. The observed variation in Jupiter’s magnetic field could provide additional constrains on the structure and speed of the zonal winds at depth. However, the interpretation of the secular variation is complicated by the fact that the electrical conductivity and thus magnetic effects increase rapidly with depth while the zonal winds decay with depth. Here we use a simple numerical model to explore the possible secular variation due to Jupiter’s zonal winds. We restrict the simulations to the outer 10% in radius and imposed the Jupiter-like magnetic field as a potential field. Different profiles for the depth dependence on electrical conductivity and winds are explore. The shear of the zonal winds increases the magnetic field dissipation over time. The dissipation seeks to balance induction and thereby reduces the secular variation. As the simulation progresses, the secular variation observed at the surface represents the zonal flow at increasing depth. The induced field also tends to significantly reduce the effective field strength at the surface. Out results suggest that the zonal flow action heavily shapes and weakens Jupiter’s magnetic field. However, the zonal flow induced secular variation would only reflect the slower flows at depth and may not contribute much to the total secular variation.</p>