The northern lights show is a wonderful sight. Since the dawn of time, it has fascinated people. More recently, researchers have theorized the origin of the phenomenon. But they had never yet been able to prove their hypotheses. It is now done thanks to physicists from the University of Iowa (United States). At least for polar aurora say of discrete form.
These are the best known. They appear as long arches, curtains of light undulating. They are produced by powerful electromagnetic waves, the Alfvén waves. They themselves are born in geomagnetic storms. And they speed up electrons around the Terre, leading them to light up in the sky these headbands of colors magical. Here is for the theory which dates from more than forty years ago. A theory supported by some satellite measurements which seem to reveal the presence of Alfvén waves traveling towards the Earth above the Northern Lights.
Result of several decades of work, a study today demonstrates experimentally the mechanisms physical of the acceleration of electrons by Alfvén waves. In their experiment, the researchers launched such waves into the chamber of the Large Plasma Device from the University of California at Los Angeles (United States). A cylinder 20 meters long and 1 meter in diameter. They then measured the acceleration of the electrons. The numerical simulations and the modelization mathematics show that the signature of this acceleration concorde well with that predicted for the Landau damping.
The depreciation of Landau? To understand, let’s go back through the story. And remember that solar flares or ejections from mass coronal can severely disrupt the flow of solar wind. Enough to trigger geomagnetic storms on Earth. They are accompanied by some of the most intense auroral manifestations. In the Earth’s remote magnetism, geomagnetic storms are at the origin of a process of magnetic reconnection. The field lines break and reform, eventually returning to Earth. Kind of like a stretched and suddenly released rubber band. This rebound of magnetic field launches Alfvén waves which travel towards our Planet along the magnetic field.
The time comes when a small population of electrons, which move in the same direction as an Alfvén wave, can be accelerated to speeds higher. The physicists speak of resonant acceleration. Like that of a surfer catching a wave. These electrons therefore surf the electric field of the Alfven wave, gaining speed thanks to this mechanism known as Landau damping – the famous … – in which theenergy of the wave is transferred to the accelerated electrons, preventing the occurrence of instability. The process was first discovered in 1946.
The electrons then travel at speeds of up to 20,000 km / s. They descend along the Earth’s magnetic field and eventually collide with the atoms and molecules oxygen andazote in L’air rarefied upper atmosphere. A meeting that gives birth to these magnificent curtains of light which then sparkle in the polar sky.
Aurora Borealis over Bear Lake, Alaska Aurora Borealis over Bear Lake in US Air Force Base Eielson, Alaska. © Wikipedia, DP
Aurora Borealis in Greenland An aurora borealis in Greenland. © Nick Russill from Cardiff, UK, CC by 2.0
Aurora Borealis in Canada This beautiful photo of the aurora borealis is available as a wallpaper on the Canadian Space Agency website. © AuroraMax
Aurora Borealis over Lake Ennadai, Canada Aurora borealis photographed at Ennadai Lake, located in the Kivalliq region, Nunavut (Canada). © Alan D. Wilson, CC by-sa 3.0
Aurora borealis in green colors, Canada Aurora borealis over Ennadai Lake, Kivalliq region, Nunavut (Canada). © Alan D. Wilson, CC by-sa 3.0
Aurora Borealis in Norway Aurora borealis observed in Norway. © Rafal Konieczny, Wikimedia Commons, GFDL, CC by 2.5
Aurora Borealis over Jökulsárlón, Iceland Aurora borealis above Jökulsárlón, a sumptuous lake in Iceland. © Moyan Bren, Wikimedia Commons, CC by 2.0
Aurora Borealis in Nunavut Aurora borealis photographed at Ennadai Lake, located in the Kivalliq region of Nunavut (Canada). © Alan D. Wilson, CC by-sa 3.0
Aurora Borealis in Austurland, Iceland Aurora Borealis in Austurland, Iceland. © Caillum Smith, Wikimedia Commons, CC by-sa 3.0
Aurora Borealis photo in Greenland Aurora borealis photographed in Greenland. © Greenland Travel, Wikimedia Commons, CC by 2.0
Aurora Borealis in Iceland Aurora Borealis in Iceland. © Theo Schacht, Wikimedia Commons, CC by-sa 3.0
Aurora Borealis Photo in Canada Aurora Borealis in Canada. © Kshitijr96, Wikimedia Commons, CC by-sa 3.0