Galactic cosmic ray modulation at high rigidities: cycles 20 – 22 and the ascending phase of cycle 23 Original Research Article

We have followed the long term, steady state, 11 year modulation of the galactic cosmic ray (GCR) intensity for several solar cycles, using the dataset obtained with a variety of detectors on Earth (neutron monitors and ion chambers, at different global sites) as well as at the balloon altitudes. The median rigidity of response (Rm) for these detectors, to GCR spectrum, lies in the range: 3 GV < Rm < 67 GV. The onset of modulation for cycle 23 occurred at Earth following a number of coronal mass ejections in the April–May 1998 period, as an active region moved across the solar disk from the east to the west limb. We have examined the characteristics of the observed modulation at Earth so far and compared it with those observed previously at the relatively comparable stages of development. Although the modulation pattern is the same for all the cycles studied, the contributions to the amplitude of modulation as a function of the phase of solar activity vary greatly from one cycle to another.