“Surfing” particles: physicists solve a mystery surrounding the Northern Lights
Experiments confirm the interaction of electrons and Alfvén waves
June 21, 2021
The spectacularly colored Northern Lights – or Northern Lights – that fill the skies in high latitude regions have fascinated people for thousands of years. Today, a team of scientists has solved one of the last mysteries surrounding its origin.
Researchers know that electrons and other energized particles, which emanate from the sun as part of the “solar wind,” accelerate the Earth’s magnetic field lines and reach the upper atmosphere. There, they collide with molecules of oxygen and nitrogen, propelling them into an excited state. These molecules then relax by emitting light, producing the beautiful green and other hues of dawn.
What has not been fully understood is precisely how groups of electrons accelerate through the magnetic field on the last leg of their journey, reaching speeds of up to 45 million mph. In a study published in Nature Communications, physicists from the University of California at Los Angeles, Wheaton College, the University of Iowa, and the Space Science Institute answered the question.
One popular theory has been that electrons hitchhike on Alfvén waves – electromagnetic waves that spacecraft have frequently identified traveling to Earth along magnetic field lines above the aurora. While space research has strongly supported the theory, limitations inherent in spacecraft measurements have prevented a definitive test.
To overcome these limitations, physicists conducted laboratory experiments at UCLA’s Basic Plasma Science Facility, supported by the US National Science Foundation and the US Department of Energy. The research is the first direct test showing that Alfven waves can produce accelerated electrons that cause aurora.
Vyacheslav (Slava) Lukin, program director in the physics division of the NSF, said that “this experimental confirmation of the physics behind the aurora is due to the ingenuity of the research groups at the University of Iowa and UCLA. From student support through an NSF Graduate Fellowship, to the NSF CAREER program for early career faculty, to the 25-year partnership between NSF and the Department of Energy which has enabled The unique capabilities of the Basic Plasma Science Facility, this is a discovery made possible by the continued support of the academic research community.
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