Evidence for charge drift modulation at intermediate solar activity from the flux variation of protons and alpha particles

We have studied the flux of galactic protons and helium nuclei measured at 1 AU along two consecutive solar activity cycles. We have correlated cosmic ray fluxes measured on IMP 8 satellite at low energy (50 - 300 MeV amu(-1)) with neutron monitor counts registered at Climax station (at energies above few GeV) during the period 1973 - 1995. We have found a systematic excess in the flux of the positive charged particles during the periods with positive solar magnetic field polarity (A > 0) with respect to the flux during the periods of negative polarity (A < 0). This flux excess gives an experimental evidence that charge drift effect plays an important role in the modulation of galactic cosmic rays. A systematic investigation of charge drift modulation is presented. The dependence of the drift effect on the solar activity phase and the particle energy has been also studied. A variation of the proton (as well as helium) flux might be as large as 40%, at the solar activity minimum of two contiguous cycles, at energy less than or equal to 100 MeV