The March 1991 Storm and the Third Radiation Belt

What happened

A very fast coronal mass ejection from an X9.4 flare compressed Earth's magnetosphere within minutes of arrival, and NASA's CRRES satellite observed the formation of an entirely new, temporary third radiation belt of energetic protons between the traditional inner and outer Van Allen belts. The event reshaped scientific understanding of how quickly the near-Earth radiation environment can be re-engineered by a single CME.