Last week’s solar flare and mass ejection presented a real risk, but the effects predicted didn’t materialize — why?
The storm was so weak because the flare’s magnetic field happened to be aligned parallel to the Earth’s. When the sun sends a mass of hot plasma hurtling toward the planet in a coronal mass ejection, the plasma is imprinted with its own magnetic field separate from the sun’s. Astronomers can’t predict the direction of the plasma’s magnetic field until the burst hits Earth.
If the plasma’s magnetic field is parallel to the Earth’s, the incoming charged particles are effectively blocked from entering Earth’s magnetosphere. An identical flare with a perpendicular magnetic field would have triggered a much stronger storm.
As they note, this amounted to dodging a bullet.