Mystery of Northern Light Bursts Finally Solved

December 22, 2015 | Joanne Kennell

Photo of bright green and red aurora against a starry night sky
Photo credit: FairbanksMike/Flickr (CC BY 2.0)

“This isn't like anything that us space physicists had in mind.”

If you are lucky enough to have seen either the Aurora Borealis or Aurora Australis, you know how breathtaking they can be.  They are always present in the polar regions, although dimly throughout the night, and only sometimes blow up the sky with vibrant shades of green, red and blue.  But have you ever wondered what causes these lights to suddenly get so bright and vivid?

It is a process called auroral breakup.  This breakup triggers the formation of auroral substorms and subsequent bursts of light, and scientists have been trying to uncover the mystery behind this phenomenon for years.

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A Japanese research team from Kyoto University have discovered, surprisingly, that hot charged particles, also known as plasmas, come together in near-Earth space — just above the upper atmosphere in the polar regions — when magnetic field lines reconnect in space.  This reconnection makes the particles rotate which creates a sudden electrical current, and this current is discharged creating a “surge” of extra electricity (shown in the image below).  This “surge” creates the bright sparks of light that characterize auroral substorms.  

“This isn't like anything that us space physicists had in mind,” said study author Yusuke Ebihara of Kyoto University.

a golden ring thousands of kilometers wide, encircling  magnetic north (somewhere in Northern Canada)
photo credit: Kyoto University

Auroras originate from plasma from the sun, also known as solar wind, and it was discovered in the 1970s that, when this plasma approaches Earth and interacts with magnetic fields, it triggers a change in magnetic field lines.  However, this was not enough to explain the sporadic bursts of light.

Scientists had previously theorized a couple processes such as it being caused by the acceleration of plasma from the magnetic field lines, or that an electrical current running near the Earth could divert some of the electrical current into the ionosphere.  The second theory was the most widely accepted, however it still was not a perfect explanation — something was missing.

Ebihara used a supercomputer simulation developed by Takashi Tanaka, professor emeritus at Kyushu University, for the study, and the results offered a clear explanation for the phenomenon.  “Previous theories tried to explain individual mechanisms like the reconnection of the magnetic field lines and the diversion of electrical currents, but there were contradictions when trying to explain the phenomena in its entirety,” said Ebihara. “What we needed all along was to look at the bigger picture.”

Now that researchers finally understand what causes these auroral substorms, the next stage of the research involves looking into alleviating problems associated with these breakups including the disruption of satellites and power grids.

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