Protons with kinetic energy E > 70 MeV trapped in the Earth's radiation belts

Accurate measurements of under cutoff proton fluxes in the energy range 0.07–9.1 GeV have been performed with the Alpha Magnetic Spectrometer (AMS) at altitudes of 370–390 km in the geographic latitude interval ±51.7°. A clear transition from a Stably Trapped population typical of the Inner Van Allen belts, in the region of the South Atlantic Anomaly (SAA), to a Quasi‐Trapped population in the regions underneath the Van Allen belts outside the SAA is observed. The flux maps as a function of the canonical adiabatic variables L, α o , and energy E are presented and discussed.