![]() ![]() However, because the CRAND source for the trapped protons comes mostly from low geomagnetic latitudes (high cutoff rigidities), the solar modulation of the parent cosmic rays has a relatively small effect on their variability (Selesnick et al. Protons with energies in excess of a few tens of MeV mostly originate through the Cosmic-Ray Albedo Neutron Decay (CRAND) mechanism (Singer 1958 Farley & Walt 1971). In general, both source and loss processes associated with inner-belt protons experience long-term variations during the solar cycle. Specifically, the low-altitude geomagnetically trapped proton population is known to be coupled to the atmospheric neutral density through changes induced by solar activity. Besides constituting a significant hazard to human activities in space, the intense fluxes of charged particles trapped in the radiation belts influence the chemical balance and energy budget of the upper atmosphere that, in turn, strongly impact on the dynamics of magnetospheric particles. The main contribution to the radiation exposure comes from the passage through the so-called South Atlantic anomaly (SAA), where the inner Van Allen belt reaches its minimum distance from the terrestrial surface. The low-altitude (≲1000 km) region is of special interest to the modeling of the near-terrestrial space environment, given the numerous robotic and manned missions in low Earth orbit (LEO). University of Udine, Department of Mathematics, Computer Science and Physics, Via delle Scienze, 206, Udine, Italy Istituto Nazionale di Astrofisica, Fosso del cavaliere 100, I-00133 Rome, Italy INFN, Laboratori Nazionali di Frascati, Via Enrico Fermi 40, I-00044 Frascati, Italy Universitat Siegen, Department of Physics, D-57068 Siegen, Germany University of Trieste, Department of Physics, I-34100 Trieste, Italy MEPhI: National Research Nuclear University MEPhI, RU-115409, Moscow, Russia IFAC, I-50019 Sesto Fiorentino, Florence, Italy RIKEN, EUSO team Global Research Cluster, Wako-shi, Saitama, Japan KTH, Department of Physics, and the Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, SE-10691 Stockholm, Sweden Ioffe Physical Technical Institute, RU-194021 St. INFN, Sezione di Trieste, I-34149 Trieste, Italy University of Bari, Department of Physics, I-70126 Bari, Italy Lebedev Physical Institute, RU-119991, Moscow, Russia INFN, Sezione di Naples, I-80126 Naples, Italy University of Naples "Federico II", Department of Physics, I-80126 Naples, Italy INFN, Sezione di Florence, I-50019 Sesto Fiorentino, Florence, Italy University of Florence, Department of Physics, I-50019 Sesto Fiorentino, Florence, Italy INFN, Sezione di Bari, I-70126 Bari, Italy ![]() INFN, Sezione di Rome "Tor Vergata", I-00133 Rome, Italy University of Rome "Tor Vergata", Department of Physics, I-00133 Rome, Italy Heliophysics Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA of Physics, Catholic University of America, Washington, DC 20064, USA ![]() ![]() Solar-cycle Variations of South Atlantic Anomaly Proton Intensities Measured with the PAMELA MissionĪ. ![]()
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