Physicists have found a correlation between plasma waves in the Earth's magnetosphere and the appearance of the northern lights. The scientists confirmed their assumption using radar and satellite observations, revealing a link between the increased activity of electrostatic cyclotron harmonic waves in the magnetosphere and the appearance 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 disturbances of various kinds in the Earth's atmosphere: due to the large amount of energy received from the Sun, strong electric fields arise in the airspace, and these, in turn, excite plasma turbulence. Such magnetospheric processes affect the ionosphere due to two main factors: first, with the help of scattered electrons, which create a quasi-constant electric field, and second, due to local ionization of the plasma, which modulates the conductivity of the medium. For example, the Farley-Buneman instability appears when the relative drift between strongly 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 satellite ARASE and the Canadian aurora detector ICEBEAR. The scientists found 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 often occur.
Physicists formulated the conditions that preceded the detected event: due to a nine-fold jump in the dynamic pressure of the solar wind, a strong impulse compressed the Earth's magnetosphere. It, in turn, initiated a flow of electrons that created strong electric fields and a plasma density gradient due to gas ionization. In addition, scientists noted that the detected pulsating aurora retained the temporal and spatial characteristics of the ensembles of interacting waves and particles that generated them, and also demonstrated a self-similar structure up to meter scales.
The authors of the paper emphasized that their interpretation of the surge in ionospheric activity should improve existing space weather models, since predictions of events in the lower atmosphere can be made more accurate by observing the magnetosphere.
We wrote earlier about how the glow of the steves, pinkish-purple phenomena similar to the polar lights, was explained independently of the accompanying “green fence”.