The prime suspect is an unexpected CME embedded in the solar wind.
Space weather expert Dr Tamitha Skov said on Twitter on Saturday, “Fast solar wind hits Earth.These natural light shows are generated when particles from the solar wind excite atoms in Earth’s upper atmosphere, which makes them glow.Another type of solar storm is solar flares."The explosive heat of a solar flare can't make it all the way to our globe, but electromagnetic radiation and energetic particles certainly can," NASA explained.