Jonathan Nackstrand / AFP via Getty Images
Nothing can spoil our joy in the Northern Lights, or Northern Lights, those ribbons of blue, green and purple light that cascade from the sky. Not even knowing for sure what is causing them.
Physicists have long speculated on what is behind this very specific light phenomenon that occurs in the polar regions of the Earth.
Now they are certain.
A item published in the journal Nature Communication this week suggests that the natural light show begins when disturbances on the sun pull on the Earth’s magnetic field. This creates cosmic ripples known as AlfvÃ©n waves which launch electrons at high speed into Earth’s atmosphere where they create the aurora.
âIt’s been sort of theorized that this is where the energy exchange occurs,â said Gregory Howes, associate professor of physics and astronomy at the University of Iowa. “But no one had ever made a definitive demonstration that Alfven waves actually accelerate these electrons under the proper conditions you have in space above aurora.”
How the dawn is formed
The sun is volatile and violent events, such as geomagnetic storms, can reverberate through the universe.
In some cases, the sun’s disturbances are so strong that they cling to the earth’s magnetic field like a rubber band, pulling it away from our planet.
But, like a tight rubber band when released, the magnetic field returns and the force of that recoil creates powerful ripples known as Alfven waves about 80,000 miles above the ground. As these waves get closer to Earth, they travel even faster thanks to the planet’s magnetic pull.
On the same space highway, electrons also travel to Earth, but not as fast as the AlfvÃ©n waves.
Sometimes electrons hitchhike on these super-fast AlfvÃ©n waves, reaching speeds as high as 45 million miles per hour as they hurtle downward.
âThink about surfing,â said Jim Schroeder, physics professor at Wheaton College and lead author of the article. âTo surf you have to paddle at the right speed for an ocean wave to lift you up and speed you up, and we found that electrons surf. If they were moving at the right speed relative to the wave, they would. be picked up and sped up. “
Austin Montelius / College of Liberal Arts and Sciences, University of Iowa
When electrons reach the top thin layer of the Earth, they collide with molecules of nitrogen and oxygen, sending them into an excited state. The excited electrons eventually calm down and release light, which we think of as dawn.
What experience has shown
While scientists have believed for decades that Alfven waves were responsible for accelerating electrons, this lab experiment produced the only definitive evidence.
âNo one has ever measured this between electrons and AlfvÃ©n waves before,â Schroeder told NPR.
The researchers used what is called the Large Plasma Device at UCLA’s Basic Plasma Science Facility to recreate the interaction between AlfvÃ©n waves and electrons.
Such a study would have been impossible in space given that the researchers cannot predict when the auroras will occur and would not be able to account for other factors in the cosmos, they said.
The researchers suggested that their findings could help understand more broadly how particles are energized and also give them a clearer picture of how events on the sun affect near-Earth space as well as the technological infrastructure that we have there, like satellites.
Another much simpler advantage for Schroeder is this type of research.
âIt appeals to our sense of awe and wonder,â he said. âWe have been captivated by auroras for thousands of years and gaze at the night sky and appreciate their beauty. And I have always found that better understanding how something is created enhances my appreciation of that beauty.â