Magnetic Effects of Plasma Pressure Gradients in the Upper F Region

TL;DR

This paper demonstrates that plasma pressure gradients cause magnetic perturbations in the upper F region, revealing a ubiquitous diamagnetic current at polar latitudes that influences small-scale magnetic field variations.

Contribution

It shows that plasma pressure gradients induce diamagnetic currents at polar latitudes, a phenomenon previously thought to be limited to equatorial regions.

Findings

Plasma pressure gradients produce measurable magnetic perturbations.

Diamagnetic currents are prevalent at polar latitudes.

Small-scale magnetic variations are dominated by these effects.

Abstract

The Swarm satellites fly at altitudes that at polar latitudes are generally assumed to onlycontain 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 x 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.