On Christmas Day in 2022, a rare and smooth aurora appeared over the Arctic, unlike any seen before. Researchers from Japan and the US discovered that this unique aurora was caused by a ‘rainstorm’ of electrons from the sun. This phenomenon, known as the polar rain aurora, had never been observed from the ground until now.
Typically, auroras display distinct patterns and movements in the sky, powered by electrons from the solar wind interacting with Earth’s magnetic field. However, the aurora observed on December 25-26, 2022, was featureless and stretched over 2,485 miles without any structure or variation in brightness. This puzzling aurora puzzled scientists until they compared ground observations with satellite data.
Satellite imagery confirmed that the smooth aurora was, in fact, a polar rain aurora, a rare type that had only been seen from space previously. This unique aurora was caused by electrons streaming from a coronal hole on the sun, reaching Earth’s magnetic field above the north pole. The absence of regular solar wind allowed these high-energy electrons to create the smooth and green auroral emission.
The diameter of the magnetic funnel opening from the sun was so wide that it covered a larger area than Earth’s north polar cap, resulting in the aurora appearing smooth and featureless. The unique green color of the aurora was due to the high energy of the electrons ionizing oxygen in the atmosphere.
This discovery sheds light on a phenomenon that was previously studied mainly through satellite observations. The polar rain aurora, normally invisible from the ground, became visible due to the unusual conditions of decreased solar wind pressure. This groundbreaking research provides new insights into the interaction between the sun’s electrons and Earth’s magnetic field during a rare and spectacular event.
