Laboratory Experiments Confirm the Polarization of Auroral Emissions.

A series of experiments have shown recently that several auroral lines are polarized, when observed from the ground. However, this polarization may be caused by indirect light sources (from the ground or the sky) scattered in the lower atmosphere by Rayleigh and Lorenz‐Mie scattering, or during the crossing of the ionospheric current sheets. Here, we present polarization measurements of the N2+ ${N}_{2}^{+}$ blue (427.8 nm) and purple (391.4 nm) emissions in a laboratory confined setting that excludes any light pollution or scattering. We show that both lines are polarized, at a level comparable to that of the natural auroral observations. Our results furthermore show that the Degree of Linear Polarization depends on the magnetic conditions. This set of experiments confirms in a controlled environment the polarization of auroral emissions and constitutes a strong evidence in favor of auroral emission already polarized in the upper atmosphere. Plain Language Summary: We prove through a laboratory experiment the existence of the auroral polarization. We also show that this polarization is created at the emission itself and not during its travel through the atmosphere. Key Points: We reproduce in confined laboratory conditions the auroral blue and purple ionospheric emissionsThe Degree of Linear Polarization depends on the magnetic conditions and is similar to that observed in the auroraeWe conclude that part of the observed auroral lights polarization is created at the emission [ABSTRACT FROM AUTHOR]