Adriani, O.O.AdrianiBarbarino, G. C.G. C.BarbarinoBazilevskaya, G. A.G. A.BazilevskayaPicozza, P.P.PicozzaRicci, M.M.RicciDi Felice, ValeriaValeriaDi Felice2020-09-172020-09-172015-04-01https://hdl.handle.net/20.500.13025/4398eprint arXiv 1504.06253We present a precise measurement of downward-going albedo proton fluxes for kinetic energy above $sim$ 70 MeV performed by the PAMELA experiment at an altitude between 350 and 610 km. On the basis of a trajectory tracing simulation, the analyzed protons were classified into quasi-trapped, concentrating in the magnetic equatorial region, and un-trapped spreading over all latitudes, including both short-lived (precipitating) and long-lived (pseudo-trapped) components. In addition, features of the penumbra region around the geomagnetic cutoff were investigated in detail. PAMELA results significantly improve the characterization of the high energy albedo proton populations at low Earth orbits.Astrophysics - High Energy Astrophysical PhenomenaPhysics - Space Physics Comment 28 pages8 figures. Accepted for publication in Journal of Geophysical Research - Space Physicshttp://adsabs.harvard.edu/abs/2015arXiv150406253A2015arXiv150406253A