Scientists believe they have confidently proven the formation mechanism behind the aurorae, the northern and southern lights visible in the night sky at higher latitudes. In particular, researchers have recreated the mechanism in the lab. It all points out to a single culprit: Powerful magnetic waves known as Alfvén waves that accelerate electrons traveling on the magnetic field lines of the Earth before slamming on the atmosphere.
As reported in Nature Communications, the team used the Large Plasma Device to recreate the waves. They witnessed as electrons were able to not only travel over those waves but to take energy from them, accelerating. These electrons can reach around six percent of the speed of light and by slamming into oxygen and nitrogen atoms, they create the colorful waving curtain effect we see in aurorae.
The experiment was far from easy. To recreate the space conditions, they had only a small number of electrons within this plasma, hoping that the moving electrons would show the characteristic signature of the so-called Landau damping as they accelerated.
“Measurements revealed this small population of electrons undergoes 'resonant acceleration' by the Alfven wave's electric field, similar to a surfer catching a wave and being continually accelerated as the surfer moves along with the wave,” co-author Professor Greg Howes, from the University of Iowa, said in a statement.
The theoretical framework for this scenario spans multiple decades, and there have been computer simulations and observations of the aurorae from Earth and space that give credence to the mechanism. The experiments conducted here add a new layer of evidence.
The mechanism of electrons surfing the Alfvén waves is now been confirmed by theory, simulations, and these latest lab results. Understanding the spectacular light shows helps us understand space weather better and the risk from geomagnetic storms.
“For a long time, the start of the auroral process with violent activity at the Sun and the end, with electrons crashing into the upper atmosphere to give off light, have been known. What has remained unknown are the steps in between. This finding supplies an important piece of the puzzle,” first author Dr. Jim Schroeder of Wheaton College said in a statement. “Understanding the physics of near-Earth space is practical, too. Our society has become dependent on this region of space, heavily populated with satellites, for communication and navigation, and the dynamics of geomagnetic storms and the aurora can adversely impact those satellites.”