Physicists have discovered a correlation between plasma waves in the Earth's magnetosphere and the occurrence of the aurora borealis. The scientists confirmed their hypothesis using radar and satellite observations, revealing a link between increased activity of electrostatic cyclotron harmonic waves in the magnetosphere and the emergence of meter-scale plasma turbulence in the lower layers of the ionosphere. The results of the study were published in Physical Review Letters.
The solar wind causes a variety of disturbances in the Earth's atmosphere: the large amount of energy received from the Sun generates strong electric fields in the air, which in turn generate plasma turbulence. These magnetospheric processes affect the ionosphere through two main factors: first, through scattered electrons, which create a quasi-constant electric field, and second, through local plasma ionization, which modulates the conductivity of the medium. For example, the Farley-Buneman instability occurs when the relative drift between highly magnetized electrons and demagnetized ions exceeds the local ion-sound velocity.
Magnus Ivarsen from the University of Oslo, together with his colleagues from the UK, Canada, Norway, South Korea and Japan, suggested that the turbulent structuring of electric fields in the lower layers of the ionosphere is caused by the interaction of waves and particles in the so-called diffuse aurora – that is, magnetospheric wave activity.
To test their hypothesis, the physicists analyzed data obtained from January 2020 to June 2023 by the Japanese ARASE satellite and the Canadian ICEBEAR aurora detector. The scientists identified the only suitable event during this period—a diffuse pulsating aurora that appeared on May 12, 2021—and analyzed its electric field power spectrum at frequencies from 0.1 to 20 kilohertz—the range in which electrostatic cyclotron harmonic waves most frequently occur.
Physicists have identified the conditions that preceded the detected event: a ninefold jump in the solar wind's dynamic pressure caused a strong pulse to compress the Earth's magnetosphere. This, in turn, triggered a flow of electrons that created strong electric fields and a plasma density gradient due to gas ionization. Furthermore, the scientists noted that the detected pulsating aurora retained the temporal and spatial characteristics of the ensembles of interacting waves and particles that generated it, and also demonstrated a self-similar structure down to meter scales.
The authors of the study emphasized that their interpretation of the surge in ionospheric activity should improve existing space weather models, as predictions of events in the lower atmosphere can be made more accurate thanks to magnetospheric observations.
We previously wrote about how the glow of the steves—pinkish-purple phenomena similar to the aurora borealis—was explained independently of the accompanying "green fence."
