Control of the innermost electron radiation belt by large‐scale electric fields. Issue 9 (10th September 2016) - Selesnick, R. S.
Abstract: Electron measurements from the Magnetic Electron Ion Spectrometer instruments on Van Allen Probes, for kinetic energies ∼100 to 400 keV, show characteristic dynamical features of the innermost ( L ≲ 1 . 3 ) radiation belt: rapid injections, slow decay, and structured energy spectra. There are also periods of steady or slowly increasing intensity and of fast decay following injections. Local time asymmetry, with higher intensity near dawn, is interpreted as evidence for drift shell distortion by a convection electric field of magnitude ∼0.4 mV/m during geomagnetically quiet times. Fast fluctuations in the electric field, on the drift time scale, cause inward diffusion. Assuming that they are proportional to changes in K p, the resulting diffusion coefficient is sufficient to replenish trapped electrons lost by atmospheric scattering. Major electric field increases cause injections by inward electron transport. An injection associated with the June 2015 magnetic storm is consistent with an enhanced field magnitude ∼5 mV/m. Subsequent drift echoes cause spectral structure. Key Points: Trapped electron local time dependence for L ≲ 1 . 3 requires an average electric field ∼0.4 mV/m Electric field fluctuations cause inward diffusion that maintains ∼100‐400 keV electron intensity Major field increases cause electron injections and structured energy spectra (zebra stripes)