Laboratory experiment on region-1 field-aligned current and its origin in low-latitude boundary layer

TL;DR

This study investigates the origin of region-1 field-aligned currents in the low-latitude boundary layer of the magnetosphere through laboratory experiments, revealing their association with azimuthal magnetic fields and wave phenomena.

Contribution

The paper provides experimental evidence linking azimuthal magnetic fields and wave activity to the generation of field-aligned currents in the magnetosphere.

Findings

Azimuthal magnetic fields exhibit quadruple symmetry and local maxima near the boundary layer.

Presence of FACs affects the amplitude and structure of sheared magnetic fields.

FACs flow upward on the dawnside and toward the equator on the duskside, matching independent measurements.

Abstract

In previous experiments by the authors on a magnetic dipole interacting with a laser-produced plasma the generation of an intense field-aligned current (FAC) system on terrella poles was observed. In this paper the question of the origin of these currents in a low-latitude boundary layer of magnetosphere is investigated. Experimental evidence of such a link was obtained by measurements of the magnetic field generated by tangential drag and sheared stress. This specific azimuthal field was found to have quadruple symmetry and local maxima inside the magnetosphere adjacent to the boundary layer. Cases of metallic and dielectric dipole covers modeling good conductive and non-conductive ionosphere revealed that the presence or absence of FACs results in different amplitudes and spatial structures of the sheared field. The current associated with the azimuthal field flows upward at the dawnside, and toward the equator plane at the duskside. It was found to coincide by direction and to correspond by amplitude to a total cross-polar current measured independently. The results suggest that compressional and Alfven waves are responsible for FAC generation. The study is most relevant to FACgeneration in the magnetospheres of Earth and Mercury following pressure jumps in solar wind.