The contribution of compressional magnetic pumping to the energization of the Earth’s outer electron radiation belt during high-speed-stream-driven storms

Compressional magnetic pumping is an interaction between cyclic magnetic compressions and pitch-angle scattering with the scattering acting as a catalyst to allow the cyclic compressions to energize particles. Compressional magnetic pumping of the outer electron radiation belt at geosynchronous orbit in the dayside magnetosphere is analyzed by means of computer simulations, wherein solar-wind compressions of the dayside magnetosphere energize electrons with electron pitch-angle scattering by chorus waves and by EMIC. The magnetic pumping is found to produce a weak bulk heating of the electron radiation belt, and it also produces an energetic tail on the electron energy distribution. The amount of energization depends on the robustness of the solar-wind compressions and on the amplitude of the chorus and/or EMIC waves. Chorus-catalyzed pumping is better at energizing medium-energy (50 - 200 keV) electrons than it is at energizing higher energy electrons; at high energies (500 keV - 2 MeV) EMIC-catalyzed pumping is a stronger energizer. The magnetic-pumping simulation results are compared with energy-diffusion calculations for chorus waves in the dayside magnetosphere; in general compressional magnetic pumping is found to be weaker at accelerating electrons than is chorus-driven energy diffusion. In circumstances when solar-wind compressions are robust and when EMIC waves are present in the dayside magnetosphere without the presence of chorus, EMIC-catalyzed magnetic pumping could be the dominant energization mechanism in the dayside magnetosphere, but at such times loss-cone losses will be strong.