The ERG spacecraft observed chorus waves and scattered electrons in the magnetosphere, the origin of pulsation auroras. The scattered electrons precipitated into the atmosphere resulting in auroral illumination. Intermittent occurrence of chorus waves and associated electron scattering lead to auroral pulsation. Credit: 2018 ERG science team.
For the first time, a satellite has directly observed the shower of electrons bouncing across Earth’s magnetosphere, allowing scientists to figure out what causes a rare form of Northern Lights known as pulsating auroras. Typically, the Aurora Borealis is caused by charged particles released from the upper atmosphere of the Sun. When these high-speed particles smash into the Earth’s magnetosphere, they let out their energy, creating an array of beautiful green, red, and purple colors swirling and dancing in the sky. The effect is most prominently seen near Earth’s magnetic poles.
Among a variety of auroras, pulsating auroras appear at dawn. Instead of the typical swirling spectacle of the Northern Lights, these auroras appear like giant blinking patches of light in the sky. Not only do the pulsating auroras look different, but the source of their electrons differs too. “Auroral substorms… are caused by global reconfiguration in the magnetosphere, which releases stored solar wind energy,” Satoshi Kasahara, an associate professor at the University of Tokyo’s Graduate School of Science, said in a statement. “They are characterized by auroral brightening from dusk to midnight, followed by violent motions of distinct auroral arcs that eventually break up, and emerge as diffuse, pulsating auroral patches at dawn.”
It’s always been theorized that they were caused by “clumps” of plasma waves called chorus waves that shower down on the magnetosphere. However, until now, on-the-ground measuring tools have not been sensitive enough to see what’s going on. Now this theory has been directly observed. Using a specialized electron sensor onboard the Japanese Arase (ERG) Geospace Probe, a team from the University of Tokyo has observed chorus waves and the showering of electrons that bounces across Earth’s magnetosphere, the origin of pulsating auroras. Their results were recently published in the scientific journal Nature.
“We, for the first time, directly observed scattering of electrons by chorus waves generating particle precipitation into the Earth’s atmosphere,” added Kasahara. “The precipitating electron flux was sufficiently intense to generate pulsating aurora.” http://www.iflscience.com/space/weve-directly-observed-electrons-causing-pulsating-auroras-for-the-first-time/
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