Solar Modulation of Hydrogen and Helium Cosmic Ray Nuclei Spectra above 400 Mev/nucleon, from 1976 TO 1993.

Hydrogen and helium cosmic ray nuclei spectra gathered during 7 balloon flights from 1976 to 1993 have been corrected to the top of the atmosphere and normalized at high rigidities. The variation of these primary cosmic ray fluxes above 400 MeV/nucleon has been examined as a function of the phase of the solar cycle. The intensity of the normalized fluxes varies widely between solar maximum and minimum conditions, the largest variations observed being a factor of 6 for hydrogen at rigidities near 1 GV/c, and a factor of 4.3 for helium near 2 GV/c. The force-field approximation model has been used to fit the observed data, assuming interstellar power-law spectra in rigidity and solar modulation parameter Phi. The relation between the fitted modulation parameters and the corresponding Climax neutron monitor count rates can be described by Phi = Phi _0 + e^{P_1+P_2X} , where the fitted Phi_0 is (420 +/- 30) MeV for hydrogen and (541 +/- 60) MeV for helium. The parameter Phi_0 can be interpreted as the residual modulation, X is the (scaled) neutron monitor count rate, and P_1 and P _2 are additional parameters.