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Variation of Bartol neutron monitor counts and sunspot number from 1991 to 2015. The BESS, ATIC-2 and BESS-Polar flights are marked as circles at the corresponding sunspot number. The periods for which PAMELA and AMS-02 proton and helium spectra have been reported are shown as bars at the approximate average sunspot number. The BESS-Polar II flight was carried out very near the deepest solar minimum.
