First evidence of polarized emissions in pulsating aurorae

In the last decade, several instruments have been developped to measure the auroral light polarisation. However, its study has faced the issue of anthropic light pollution and scattering in the lower atmosphere (Bosse et al., 2020). To overcome this challenge, several methods were used, and until now, the most succesfull was the use of a polarised radiative transfer model (Bosse et al., 2022) to identify the light pollution contribution. However during the past year a new look at the data revealed that pulsating aurorae are polarised, and that this polarisation carries a lot of information. The main advantage of using pulsating aurorae is that the variations in the light polarisation are very fast, of the order of a few seconds. This allows us to dismiss any potential source of polarisation that are not synched with the pulsation of the aurora.

These polarisation patterns are seen in the green atomic oxygen line at 557.7 nm, the 1st N2+ negative band at 391.4 nm (purple) and 427.8 nm (blue).

There are no clear explanations on the origin of this auroral polarisation, or its relation to the local state of the upper atmosphere. An hypothesis is that this polarisation can be either created directly at the radiative de-excitation or may occur when the non-polarised emission crosses the ionospheric currents.

We will present how these new findings confirm the ionospheric origin of the polarisation observed from the ground, as well as some of the potentialities these observations and models offer in the frame of space weather, aerosol and light pollution study.