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We review comprehensive observations of electromagnetic ion cyclotron (EMIC)wave-driven energetic electron precipitation using data from the energeticelectron detector on the Electron Losses and Fields InvestigatioN (ELFIN)mission, two polar-orbiting low-altitude spinning CubeSats, measuring 50-5000keV electrons with good pitch-angle and energy resolution. EMIC wave-drivenprecipitation exhibits a distinct signature in energy-spectrograms of theprecipitating-to-trapped flux ratio: peaks at 0.5 MeV which are abrupt (bursty)with significant substructure (occasionally down to sub-second timescale).Multiple ELFIN passes over the same MLT sector allow us to study the spatialand temporal evolution of the EMIC wave - electron interaction region. Usingtwo years of ELFIN data, we assemble a statistical database of 50 events ofstrong EMIC wave-driven precipitation. Most reside at L=5-7 at dusk, while asmaller subset exists at L=8-12 at post-midnight. The energies of thepeak-precipitation ratio and of the half-peak precipitation ratio (our proxyfor the minimum resonance energy) exhibit an L-shell dependence in goodagreement with theoretical estimates based on prior statistical observations ofEMIC wave power spectra. The precipitation ratio's spectral shape for the mostintense events has an exponential falloff away from the peak (i.e., on eitherside of 1.45 MeV). It too agrees well with quasi-linear diffusion theory basedon prior statistics of wave spectra. Sub-MeV electron precipitation observedconcurrently with strong EMIC wave-driven 1MeV precipitation has a spectralshape that is consistent with efficient pitch-angle scattering down to 200-300keV by much less intense higher frequency EMIC waves. These results confirm thecritical role of EMIC waves in driving relativistic electron losses. Nonlineareffects may abound and require further investigation.

Energetic electron precipitation driven by electromagnetic ion cyclotron waves from ELFIN's low altitude perspective