After two years of rigorous study, researchers from Japan and the United States have unveiled the cause behind the mysterious green aurora that appeared in the Arctic on Christmas Day in 2022. This rare phenomenon was found to be the result of a ‘rainstorm’ of electrons directed from the Sun.
A unique celestial event
This was the first time such an unusual aurora was observed from Earth. It occurred during a period of significantly reduced solar wind, which had left the space around Earth unusually calm.
Typically, auroras move and pulsate in recognizable shapes across the sky, powered by electrons from the solar wind—a stream of charged particles emitted by the Sun. These electrons become trapped in an extension of Earth’s magnetic field known as the magnetotail.
The role of extreme space weather
During extreme space weather events, such as a coronal mass ejection (CME)—a large expulsion of plasma and magnetic field from the Sun—the magnetotail can become pinched off. This process allows trapped electrons to flow down the Earth’s magnetic field lines near the poles.
As these electrons descend, they collide with molecules in Earth’s atmosphere, causing them to emit the vibrant colors characteristic of auroras.
The aurora observed on December 25-26, 2022, differed significantly from typical displays. Captured by an All-Sky Electron Multiplying Charge-Coupled Device (EMCCD) camera in Longyearbyen, Norway, this aurora was a faint, featureless glow that stretched over 2,485 miles (4,000 kilometers). It lacked structure, pulsing, or varying brightness—attributes never before seen from Earth.
Unraveling the mystery
A team led by Keisuke Hosokawa from the Center for Space Science and Radio Engineering at the University of Electro-Communications in Tokyo uncovered the mystery behind these unusual auroras. By comparing their observations with data from the Special Sensor Ultraviolet Scanning Imager (SSUSI) on the polar-orbiting satellites of the Defense Meteorological Satellite Program (DMSP), they were able to determine the cause.
This groundbreaking research not only explains the extraordinary Christmas aurora but also enhances our understanding of the complex interactions between solar activity and Earth’s magnetosphere.