A new window for auroral observations

2023-2024
The observatory in Skibotn, Norway, is a prime location for monitoring the auroral activity. Installed in October 2024, the Polar Light Imager (PLI) can be remotely controlled from Belgium to capture high-resolution images of the aurora.

Equipped with multiple narrow-band filters targeting key auroral spectral lines, PLI plays a crucial role in studying the dynamics of the aurora. Analysing these images provides valuable insights about the properties of the precipitating electrons, responsible for these captivating northern lights.

Green and red auroras

The northern lights are one of the most striking manifestations of the Sun-Earth connection. Electrons from the solar wind can become trapped and accelerated within Earth’s magnetosphere before precipitating into the atmosphere.

When this happens, atomic oxygen emits light at 557.7 nm and 630 nm, producing green and red auroras, respectively. Additionally, ionized nitrogen (N₂⁺) emits at 427.8 nm, generating blue auroras at lower altitudes.

PLI captures auroral images

To monitor auroral activity, BIRA-IASB has developed various instruments. In collaboration with the University of Tromsø, the Polar Light Imager (PLI) was installed in October 2024. This system uses commercial cameras equipped with wide-field lenses and narrow-band filters specifically designed for this experiment. PLI captures auroral images in the three main spectral lines associated with the northern lights.

Furthermore, a fourth camera, fitted with an H-alpha filter, is used to detect proton auroras. When protons from the solar wind precipitate into Earth's atmosphere, they can recombine with electrons, forming excited hydrogen. This process leads to emissions in the H-alpha and H-beta spectral lines.

PLI Animation
Movie of the aurora as taken with PLI (.mp4)

Determining key parameters of precipitating electrons

Beyond capturing mesmerizing images, PLI plays a crucial role in determining key parameters of precipitating electrons, such as their mean energy and flux. To achieve this, electron transport models like Transsolo and Aeroplanets are used to generate look-up tables based on the ratios of spectral line emissions—for example, the red emission at 630 nm relative to the blue emission at 427.8 nm.

Using artificial intelligence, the images will soon be classified into different auroral categories, such as steady arcs, discrete auroras, and diffuse auroras. Each category corresponds to a different phase of geomagnetic storms and substorms.

These images will also be integrated into a large database to support the reconstruction of auroral volume emissions using tomography techniques.

PLI instrument
PLI instrument
Figure 1: PLI instrument installed under a dome at the Skibotn Observatory, Norway