During the winter polar nights, the aurora borealis can blaze in the sky. The dancing light seems mysterious, but there is a good theoretical explanation for it. The last piece of the puzzle of that theory has now been proven. American researchers have experimentally shown how electrons can cause this atmospheric light show. consequences Monday afternoon in Nature Connections.
Scientists have long known that the aurora borealis are associated with constant solar winds and regular solar flares, in which the sun sends charged particles – such as electrons – into space. The magnetic field that surrounds the Earth protects us from this by scattering most of the particles. However, a small percentage of the charged particles follow the lines of the Earth’s magnetic field and enter the atmosphere above the poles.
It is also known that it contains electrons that shoot out into the upper atmosphere at a speed of up to 20 thousand kilometers per hour, where they collide with nitrogen and oxygen molecules. This explosion gives nitrogen and oxygen additional energy, which they emit in the form of colored light. Collisions between 100 and 200 kilometers in the atmosphere cause mainly green light, and those above 200 kilometers turn red. This creates beautiful shades of twilight.
What scientists don’t fully understand is how electrons coming from space accelerate to the high speed at which they collide with molecules in the atmosphere. Only high velocity electrons can ensure that molecules emit auroras. “In the 1970s, the idea arose that electrons get a boost from what are called Alfvn waves,” said physicist Jim Schroeder of American University Wheaton College. These are electromagnetic waves that arise when the Earth’s magnetic field is perturbed.
Extended rubber band
“Powerful eruptions occur regularly on the surface of the Sun,” Schroeder continues. “The stream of particles being pushed toward the Earth can seriously disrupt the Earth’s magnetic field and extend magnetic field lines.” These field lines fall back into place after a while, like a rubber band being suddenly released. This creates electromagnetic waves that travel along magnetic field lines to the poles – like waves that travel through a rope when one end oscillates back and forth. These are two thousand waves.
According to a theoretical idea from the 1970s, electrons from space can surf along these two thousandths of waves. Like a surfer in the sea, electrons are moved and accelerated by waves. This thrust gives them the high speed at which they make oxygen and nitrogen emit light when they hit them.
This theory is supported by measurements from search rockets and space probes that have detected the Alfn waves above the aurora borealis. The only piece of the puzzle missing to prove the theory was to prove that these Alfvn waves are capable of accelerating electrons. This is what American researchers have now done. They used a 20-meter device – the Large Plasma Device (LAPD) – in which they generated two thousand waves and observed how the electrons in them interacted with them. Schroeder: “Our experiment showed that electrons can indeed be accelerated to twilight speeds by surfing two thousandths.”
“It’s a clever experiment and not easy to perform. The researchers are doing their best to translate the experimental results into an effect on the Earth’s magnetic field scale,” emails Torsten Neubert of the Aerospace Institute at the Technical University of Denmark (DTU), who was not involved in the study. “The result confirms popular belief, but is satisfying because it reinforces the physical theory behind the aurora borealis.”