Wednesday, 14 February 2018

Dance of auroras: First direct observation of electron frolic

The shower of electrons bouncing across Earth's magnetosphere -- commonly known as the Northern Lights -- has been directly observed for the first time by an international team of scientists. While the cause of these colorful auroras has long been hypothesized, researchers had never directly observed the underlying mechanism until now.

Dance of auroras: First direct observation of electron frolic
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]
The spectacle of these subatomic showers is legendary. Green, red, and purple waltz across the night sky, blending into one another for a fantastic show widely considered one of the great wonders of the world. Among a variety of auroras, pulsating auroral patches appearing at dawn are common but the physical mechanisms driving this auroral pulsation had so far not been verified through observation.

With the advent of a new satellite with advanced measuring tools, researchers have now identified that this wonder is caused by the hard-to-detect interaction between electrons and plasma waves. This interaction takes place in the Earth's magnetosphere, the region surrounding the Earth in which the behavior of the electric particles is usually governed by the planet's magnetic field.

"Auroral substorms ... are caused by global reconfiguration in the magnetosphere, which releases stored solar wind energy," writes Satoshi Kasahara, an associate professor in the Department of Earth and Planetary Science at the Graduate School of Science of the University of Tokyo in Japan, the lead author of the paper. "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."

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