The Northern Lights have always made people look up to the sky. Astronomers know that they are born from particles blown to Earth by solar storms. But the mechanisms behind it remain difficult to elucidate. Today, researchers have for the first time succeeded in measuring one of the suspected processes in the laboratory.
Theis a wonderful spectacle. 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 (United States). At least for say of discrete form.
These are the best known. They appear as long arches, curtains ofundulating. They are produced by powerful , the . They themselves are born in . And they speed up around the , leading them to light up in the sky these headbands of 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 mechanismsof 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 and the mathematics show that the signature of this acceleration well with that predicted for the Landau damping.
Electrons like surfers
The depreciation of Landau? To understand, let’s go back through the story. And remember thator ejections from can severely disrupt the flow of . 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 . The field lines break and reform, eventually returning to Earth. Kind of like a stretched and suddenly released rubber band. This rebound of 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 tohigher. The speak of resonant acceleration. Like that of a surfer catching a wave. These electrons therefore surf the of the Alfven wave, gaining speed thanks to this mechanism known as Landau damping – the famous … – in which the 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 theand oxygen and in L’ rarefied . A meeting that gives birth to these magnificent curtains of light which then sparkle in the polar sky.