Aurora borealis found in the northern hemisphere and aurora australis in the southern hemisphere have captivated humanity since the beginning of civilization. These natural light shows provide the closest opportunity to experience space weather – conditions caused by activity on the surface of the sun, and as such they follow solar cycle.
Auroras caused when electrons are emitted from the sun as part of ‘solar wind‘winds towards the Earth and is drawn down on the Earth’s magnetic field lines, where they then collide with oxygen and nitrogen molecules in the ionosphere – the upper atmosphere between 50 and 370 miles (80 and 600 kilometers). The absorption of energy with oxygen and nitrogen ions causes them to move to an ̵
Although scientists understand what causes the Northern Lights, it remained a mystery – how do these electrons accelerate to speeds of up to 45 million miles per hour on the last stretch of their journey into the ionosphere? A team of physicists led by the University of Iowa has now responded, their results were published online on June 7th in the journal Nature Communications.
Related: What is the ionosphere? (And who is Steve?)
Scientists have found the first conclusive evidence that electrons capture a wave – specifically Alfvén waves moving the earth down magnetic field lines over the northern lights.
Experiments performed on the Large Plasma Device (LPD) at the University of California, Los Angeles (UCLA) Basic Plasma Science Facility involved simulation of conditions in the Earth’s Northern Lights the magnetosphere – the area of space where the Earth’s magnetic field and solar wind interact. The team then launched Alfvén waves down the 65-foot (20-meter) long chamber of the plasma unit and detected whether electrons in the chamber were affected by the Alfvén waves.
“Measurements revealed that this small population of electrons is undergoing ‘resonant acceleration’ of the electric field of the Alfvén wave, similar to a surfer catching a wave and continuously accelerating as the surfer moves along the wave,” said Gregory Howes, associate professor of physics at the University of Iowa in a announcement.
Researchers measured resonant acceleration and found that it was significant enough to accelerate electrons to levels needed to create aurora screens, providing the first direct evidence that electrons surfing on Alfvén waves create aurora.
This notion of ‘surfing’ electrons was first theorized by the Russian physicist Lev Landau in 1946 and is known as Landau attenuation. In this new study, researchers have proven their theory through supporting experimental measurements, numerical simulations, and mathematical modeling.
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