Ordinary auroras are caused by electrons raining down from space, hitting Earth's upper atmosphere and making the air glow. Black auroras are the opposite. Instead of electrons raining down, electrons are propelled upward, back into space. This diagram shows what happens:
The study of black auroras is still in its infancy, and forecasters cannot yet predict when or where they might appear. Aurora watchers, the next time a geomagnetic storm erupts, be on the lookout for black.