Polar rain aurora seen from Earth

Polar rain aurora seen from Earth

Aurora Earth

Scientists have discovered that the rare Arctic aurora witnessed on Christmas Day in 2022 was caused by a “polar rain” of electrons from the sun. The unusual aurora, which appeared as a faint, featureless glow spanning approximately 2,485 miles (4,000 kilometers), was the first of its kind to be observed from Earth’s surface. Researchers from the United States and Japan, led by Keisuke Hosokawa of the Center for Space Science and Radio Engineering at the University of Electro-Communications in Tokyo, determined that the aurora was formed when solar wind gusts had significantly diminished.

This allowed an intense flux of high-energy electrons to reach Earth’s atmosphere unhindered, resulting in the smooth, green glow. Unlike typical auroras that pulsate and display distinct patterns, the polar rain aurora lacked any discernible structure or varying brightness.

Polar rain aurora observed from Earth

The electrons responsible for this phenomenon originated from a coronal hole on the sun, where the sun’s magnetic field lines are open, enabling charged particles to escape and travel through space. Normally, electrons from the solar wind become trapped in Earth’s magnetotail and eventually flow down magnetic field lines to the poles, colliding with atmospheric molecules and creating the familiar aurora displays. However, the Christmas 2022 event occurred when the solar wind had almost completely subsided, providing a direct path for the high-energy electrons to reach Earth’s magnetic poles.

Satellite imagery from the Defense Meteorological Satellite Program (DMSP) and the Special Sensor Ultraviolet Scanning Imager (SSUSI) confirmed the presence of the polar rain aurora over the north polar cap, while no similar aurora was detected at the south polar cap. The findings, published in the journal Science Advances on June 21, 2024, highlight the importance of varying space weather conditions in shaping auroral displays and contribute to a deeper understanding of auroral physics. The rare polar rain aurora, previously only observed via satellite, has now been witnessed from the ground, marking a significant milestone in the study of these captivating celestial phenomena.

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