By U.S. Department of Energy
April 30, 2022
As electrons sped up by Alfvén waves stream along the Earths magnetic field (yellow drops), they hit oxygen atoms (white dots) and particles of oxygen and nitrogen (white dumbbells) and trigger them to give off light and create the auroras. Credit: Image thanks to Austin Montelius, College of Liberal Arts and Sciences, University of Iowa
The Science
Brand-new experiments have exposed the source of the aurora borealis. Alfvén waves speeding up electrons under conditions comparable to those seen in the Earths magnetosphere have actually been shown by scientists. Ionized charged particles or plasma, one of the four kinds of matter (in addition to solid, liquid, and gas), are found in the magnetosphere that surrounds the Earth. Plasmas have residential or commercial properties that are similar to both gases and fluids, but they likewise have magnetic and electric fields. Hannes Alfvén predicted in 1942 that plasmas might support waves. These waves are now referred to as Alfvén waves.
The current experiments reveal that electrons “surf” on the Alfvén waves electrical field, a phenomenon understood as Landau damping. This means that the waves energy is transmitted to the accelerated electrons, similar to a web surfer catching a wave and being constantly accelerated as the surfer advances along with the wave. These electrons are the supreme source of the aurora borealis lighting.
The Impact
Now scientists have actually shown how electrons associated with the aurora accelerate towards the Earth, where they clash with molecules in the upper atmosphere. The new research study recreated the conditions in area above the aurora in the lab. It reveals that Alfvén waves launched by storms in the earths magnetic field can accelerate the electrons that cause the bright glow of the aurora.
Summary
The amazing displays of the aurora borealis have constantly fascinated mankind. More recently, they have recorded the attention of scientists curious to discuss this phenomenon. Researchers know that electrons from area speed up into the upper atmosphere and hit atoms and particles to produce auroral light. The cause of this electron rainfall has actually been a location of ongoing research study.
One theory is supported by the truth that researchers regularly discover powerful electro-magnetic waves called Alfvén waves traveling toward the Earth above auroras. According to this theory, Alfvén waves accelerate electrons toward Earth, triggering them to precipitate and produce auroras. Although space-based measurements offer strong assistance of this theory, the constraints of these measurements have actually prevented a definitive test.
To get rid of these restrictions, scientists carried out lab experiments on the Large Plasma Device (LAPD) at University of California, Los Angeles (UCLA) Basic Plasma Science Facility, a nationwide collective research center supported collectively by the Department of Energy and the National Science Foundation. In a laboratory experiment that recreated the conditions in Earths magnetosphere, the group introduced Alfvén waves down the LAPD chamber and after that measured the electrons sped up by the electrical field of the Alfvén waves.
Measurements exposed these particular electrons undergo resonant acceleration by the waves electric field, comparable to an internet user capturing a wave and being continuously accelerated by the wave. The research study group integrates the measurements of the waves electric field and the electrons to produce an unique signature of the electron acceleration by Landau damping.
The arrangement of experiment, simulation, and modeling provides the very first direct test revealing that Alfvén waves can produce accelerated electrons that cause the aurora.
For more on this discovery, see:
Referral: “Laboratory measurements of the physics of auroral electron velocity by Alfvén waves” by J. W. R. Schroeder, G. G. Howes, C. A. Kletzing, F. Skiff, T. A. Carter, S. Vincena and S. Dorfman, 7 June 2021, Nature Communications.DOI: 10.1038/ s41467-021-23377-5.
This research was supported by the Department of Energy Office of Science, the National Science Foundation, and the National Aeronautics and Space Administration. The Basic Plasma Science Facility is supported by a Cooperative Agreement through the Department of Energy and a grant through the National Science Foundation.
These waves are now understood as Alfvén waves.
This indicates that the waves energy is transmitted to the sped up electrons, much like a web surfer capturing a wave and being continually sped up as the surfer advances along with the wave. One theory is supported by the truth that scientists routinely find powerful electromagnetic waves called Alfvén waves taking a trip toward the Earth above auroras. Measurements revealed these particular electrons undergo resonant acceleration by the waves electrical field, comparable to an internet user catching a wave and being continuously accelerated by the wave. The research study group integrates the measurements of the waves electric field and the electrons to produce a special signature of the electron velocity by Landau damping.
