“People have known about chorus for decades. Radio receivers are used to pick it up, and it sounds a lot like birds chirping,” said Craig Kletzing, from the University of Iowa, the principal investigator of the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instruments on-board the satellites.
“It was often more easily picked up in the mornings, which along with the chirping sound is why it’s sometimes referred to as ‘dawn chorus,’” he said.
The sounds are emitted by energetic particles in the upper levels of Earth’s magnetosphere, before they get whipped around by the radiation belts circling the Earth.