Abstract Processes in the radiation belts under extreme geomagnetic conditions involve the interplay between acceleration and loss processes, both of which can be caused by wave‐particle interactions. Whistler mode waves play a critical role in these interactions, and up to now their properties during extreme events remained poorly sampled and understood. We employ extensive databases of spacecraft observations to specify their distribution. We show that under extreme geomagnetic conditions, lower‐band whistler mode chorus waves have a net effect of accelerating ultra‐relativistic electrons, which results in an increase of fluxes at multi‐MeV energies by several orders of magnitude. During future magnetic superstorms, the radiation levels in the outer zone could therefore experience a substantial increase beyond what has been previously observed during the space age.
