Ultra-relativistic 7 MeV electron acceleration during intense and long-duration substorm activity

Substorms and strong convection events occurring during high-intensity long-duration continuous auroral electrojet (AE) activity (HILDCAA) events are associated with acceleration of magnetospheric relativistic electrons. From an analysis of Van Allen Probe satellite measurements, it is shown that ~7 MeV electrons are accelerated during ~3.4–4.1 days-long HILDCAA events. The dominant acceleration process is due to wave-particle interactions between magnetospheric electromagnetic chorus waves and substorm injected ~100 keV electrons. The longer the HILDCAA and chorus last, the higher the maximum energy of the accelerated relativistic electrons. The acceleration to higher and higher energies is by a bootstrap mechanism. Due to the unusually long process associated with the electron acceleration to ~7 MeV, spacecraft controllers can be given proper advance warning to shift to other modes of operation for the protection of spacecraft electronics.