Astronomy Colloquium

A key longstanding problem in space and astrophysical plasmas is determining the mechanism that accelerates electrons to relativistic energies. It is critical to understanding the dynamics of the Van Allen radiation belts, where MeV electrons can damage spacecraft systems. We report the discovery, in STEREO S/WAVES data, of obliquely-propagating whistler-mode waves in the radiation belt with electric field amplitudes more than an order of magnitude larger than other whistlers. Simulations show that these large amplitude waves can energize an electron by an MeV in less than 0.1s, explaining the rapid enhancement in electron intensities observed between the STEREO-A and STEREO-B passages through the belt. Our results show that the usual theoretical models of electron energization and scattering via small-amplitude waves, with timescales of hours to days, are inadequate for understanding radiation belt dynamics.