Solar modulation effects on the primary cosmic radiation near solar minimum

Detailed measurements of the primary cosmicray charge and energy spectrums have been available only for the period following the last solar minimum (1954). While the balloon-borne ionization chamber results of Neher [1956, 1957] at high latitude indicated that striking increases occur in the low-energy galactic component during the time of solar minimum, it is difficult to infer charge and energy spectrums from these data. An extensive survey was undertaken by McDonald and Webber [1962, 1964] using the Cerenkov scintillator technique over the period 1955-1959. These measurements did not include the periods just before and during solar minimum when maximum ionization chamber values were recorded by Neher, and the He spectrums in general did not extend below 1.2 bv.