Auroras, also known as Northern or Southern lights depending on whether they occur near the North or South Pole, are natural displays of light in the Earth’s sky. Typically these lights are dimly present at night. However, sometimes these otherwise faint features explode in brightness and can even break up into separate glowing hallmarks, appearing as spectacular bursts of luminous manifestations. This striking and picturesque phenomenon is known as an auroral breakup.

Now, Japanese scientists have quantitatively confirmed how energetic this phenomenon can be. Using a combination of cutting-edge ground-based technology and new space-borne observations, they have demonstrated the essential role of an auroral breakup in ionizing the deep atmosphere. The research furthers our understanding of one of the most visually stunning natural phenomena.

The findings were published in Earth, Planets and Space on January 23, 2019.

The sun fires beams of charged particles, or plasma, toward Earth. Also referred to as solar winds, this plasma is mostly made up of electrons, protons and alpha particles. When these particles interact with the Earth’s magnetic field, electrical currents are carried by electrons into the Earth’s atmosphere. This reaction between the electrons and their atmospheric constituents emits light of varying color and complexity, visible as an aurora. However, little is known about how energetic the electrons can be when these lights explode into the stunning lightshows known as auroral breakups. So far, the assumption has been that electrons of a specific energy level are responsible for this rare phenomenon.

In the new study, the scientists report that, contrary to conventional thinking, a specific kind of electrons with much higher energy, called radiation belt electrons, are involved in the auroral breakup. Named after their location in the Earth’s radiation belt, radiation belt electrons had not been clearly associated with auroral breakups before. The research team based their conclusions on a dataset collected via advanced technology and simulations.

“Radiation belt electrons are released from the Earth’s magnetic field and charge the mesosphere during auroral breakup. This fact was quantitatively confirmed by both cutting-edge ground-based and new space-borne observations,” adds Ryuho Kataoka, Ph.D., associate professor at the National Institute of Polar Research and the corresponding author. “This study also provides a good example how Arase satellite and PANSY radar can collaborate to understand the connection between space and atmosphere.”

In their future research endeavors, the Professor Kataoka and his team hope to understand how the radiation belt electrons are released during the short-lasting period of auroral breakup. “The ultimate goal is to understand the interplay between auroras and radiation belts,” Professor Kataoka adds.

This research was supported by several Japan Society for the Promotion of Science-Kakenhi grants.

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