  New measurements of the cosmic ray fluxes (p, e+, e- and Helium) performed by
the Alpha Magnetic Spectrometer (AMS) during a ten days flight of space shuttle
have revealed the existence of significant fluxes of particles below the
geomagnetic cutoff. These fluxes exhibit a number of remarkable properties,
such as a He-3/He-4 ratio of order ~10, an e+/e- ratio of order ~4 and
production from well defined regions of the Earth that are distinct for
positively and negatively charged particles. In this work we show that the
natural hypothesis, that these subcutoff particles are generated as secondary
products of primary cosmic ray interactions in the atmosphere can reproduce all
the observed properties. We also discuss the implications of the subcutoff
fluxes for the estimate of the atmospheric neutrino fluxes, and find that they
represent a negligibly small correction. On the other hand the AMS results give
important confirmations about the assumption of isotropy for the interplanetary
cosmic ray fluxes also on large angular scales, and on the validity of the
geomagnetic effects that are important elements for the prediction of the
atmospheric neutrino fluxes.
