Dec. 10, 2020: As predicted, a CME (pictured below) hit Earth’s magnetic field during the early hours of Dec. 10th (1:30 UT), but the impact did not cause a geomagnetic storm. Why not? Scroll down for the answer:
Why didn’t the CME cause a storm? Every CME brings with it some magnetic field from the sun. If that magnetic field points south, it opens cracks in Earth’s magnetic field, allowing solar wind to flow inside and fuel auroras. On the other hand, if the CME’s magnetic field points north, it seals cracks in Earth’s magnetic field, blocking the solar wind and quenching storms.
This CME brought a storm-killing north magnetic field. So, even though the velocity of the solar wind in the CME’s wake flirted with a high value of 600 km/s, it was ineffective at causing geomagnetic storms and auroras.