Inner radiation belt protons during the Van Allen Probes era

Instrumentation on the twin Van Allen Probes satellites has provided a completepicture of proton radiation belt structure and variability over the last fouryears. Particle intensity has been lower than expected on the basis of earliermeasurements, partly because the new data set is less susceptible to backgroundcontamination by higher energy protons, but also because of the paucity inrecent years of intense solar proton events that are a principal source ofradiation belt protons with kinetic energies below 100 MeV. Nevertheless,observations of slowly changing intensity levels provide new constraints ontrapped proton transport and loss coefficients. Combined with source rates fromalbedo neutron decay and solar proton trapping, these in turn provide stringentnew tests of current radiation belt theory.