Magnetic Effects of Plasma Pressure Gradients in the Upper F Region

The Swarm satellites fly at altitudes that at polar latitudes are generally assumed to only contain currents that are aligned with the local magnetic field. Therefore, disturbances along the main field direction are mainly signatures of auroral electrojet currents, with a relatively smooth structure due to the distance from the currents. Here we show that superimposed on this smooth signal is an irregular pattern of small perturbations, which are anticorrelated with the plasma density measured by the Langmuir probe. We show that the perturbations can be remarkably well reproduced by assuming they represent a j × B force, which balances the plasma pressure gradient implied by the density variations. The associated diamagnetic current, previously reported to be most important near the equator, appears to be a ubiquitous phenomenon also at polar latitudes. A spectral analysis indicates that this effect dominates magnetic field intensity variations at small‐scale sizes of a few tens of kilometers. Plain Language Summary The Swarm satellites fly at altitudes that at polar latitudes are generally assumed to only contain currents that are aligned with the local magnetic field. Therefore, disturbances in the magnetic field strength are mainly signatures of horizontal currents below the satellites. Such disturbances have a smooth structure due to the distance from the currents. Here we show that superimposed on this smooth signal is an irregular pattern of small perturbations, which are anticorrelated with the local plasma density. We show that this anticorrelation can be explained in terms of pressure balance between particles and the magnetic field. The electric currents that are associated with the magnetic field fluctuations, diamagnetic currents, have previously been reported to be most important near the equator. Our results show that they are a ubiquitous phenomenon at all latitudes and indicate that the diamagnetic effect dominates magnetic field intensity variations at small‐scale sizes of a few tens of kilometers. Key Points Magnetic intensity variations associated with plasma pressure are ubiquitous in the polar F region Plasma pressure effects are the dominating source of ‖B‖ variations at small spatial scales This finding may enable new ways of estimating ion temperature and plasma flow with Swarm data