ALBERT

Description: The Sun is the dominant energy source for ionizing atmospheric material and energizing a fraction of it to energies above the gravitational binding energy. Maggiolo et al. (2022) recently showed that, for current conditions, the solar wind energy dissipated in the Earth’s upper atmosphere is higher than it would be if the Earth were not magnetized. Indeed, despite shielding the atmosphere from the solar wind, the Earth’s magnetosphere has a much larger cross section with the solar wind than the planet itself. It thus dramatically increases the size of the interaction region between the solar wind and the planetary environment and thus the amount of solar wind energy that can potentially be diverted toward the upper atmosphere.In this study, we investigate the effect of the Earth’s magnetosphere on the solar wind energy dissipation in the atmosphere during the last 4 billion years, when the Sun was more active. The solar wind density and velocity were higher in the past which has two opposite effects. On the one hand, the Earth’s magnetosphere was more compressed by the higher solar wind pressure, reducing its cross section with the solar wind. On the other hand the solar wind energy flux density was higher. We use physical considerations and extrapolate current measurements to constrain the role of the Earth’s magnetosphere on the energy coupling between the solar wind and the upper atmosphere for such conditions.

Description: Recent observations with spectro-photo-polarimeters have shown that the auroral emissions from oxygen at 577.7 nm (green line), and from the N2+ 1st negative band emissions at 427.8 nm (blue line) and 391.4 nm (purple line) are polarized at a few percent level and that this polarization is linked to geomagnetic activity and cannot be explained by light pollution only. The origin of this polarization is still puzzling and could be related to ionospheric currents, either field-aligned or horizontal Pedersen/Hall currents.In November 2022, we set-up a multi-instrument observing campaign in Norway in order to better understand this situation. At the Skibotn observatory, we used two instruments dedicated to the measurements of auroral light polarization : PLIP, a Polar Lights Imaging Polarimeter, able to measure polarization of the three main auroral emissions (green, red and blue) on a large FOV (~44° × 30°) on the sky, and Corbel Cru, a spectro-photo polarimeter able to measure faint polarized signals in a 2° FOV in the green, blue and purple line. These data were complemented by optical observations from the ALIS_4D network in Sweden in order to obtain 2D precipitating electron fluxes using tomographic-like inversion techniques, and by radar observations with the EISCAT UHF antenna working in scanning mode. In this contribution we will present preliminary results from these instruments for a good case study obtained during this campaign. One goal of the campaign is to check whether the angle of linear polarization can be used as tracers for ionospheric currents.

Description: 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 the most succesfull method was the use of a polarised radiative transfer model to identify the light pollution contribution (Bosse et al., 2022). This year, a new look at the data revealed that pulsating aurorae are polarised, and that this polarisation carries a lot of information. Searching for polarisation in pulsating aurorae allows us to dismiss any external source of polarisation that is not synched with the pulsation of the aurora. Thus light pollution is not a problem anymore.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). Today, 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, and discussing about the opportunities these observations and models offer in the frame of space weather, aerosol and light pollution study.

Description: Understanding atmospheric escape into space for stellar and planetary conditions differing from the current ones on Earth is an ongoing challenge. It helps us to assess the stability of planetary atmospheres, hence their habitability. Over geological time scales, despite the small changes in Earth’s magnetic field magnitude, the solar wind pressure, and EUV radiation from the Sun have evolved significantly, affecting the atmospheric erosion rate. On one hand, the solar wind pressure affects non-thermal processes, and on the other EUV radiation alters Earth’s atmospheric parameters, increasing the ion production rate and the exospheric temperature. Both jointly cause a significant effect on erosion. We developed a semi-empirical model to analyze seven different erosion mechanisms and their dependency on terrestrial and solar parameters, in order to estimate the oxygen escape rate for past conditions. Our model considers variations of the Earth’s magnetic moment, the solar wind pressure, and the solar EUV flux. We discuss the effect of different atmospheric factors and their impact on the oxygen loss for each escape process and provide an estimate of the total amount of oxygen lost by the Earth over the last ~2 billion years. In addition, such a model contributes to identifying the solar and planetary parameters that are critical for the stability of the planet’s atmosphere.