RADIAL AND LATITUDINAL GRADIENTS IN GALACTIC COSMIC-RAYS

We have deduced the yearly averaged value of the solar diurnal variati on as observed by a surface muon telescope and three underground muon telescopes over the years 1957 to 1985. This has allowed us to examine the temporal variation in both the latitudinal gradient G(z) and the product of the parallel mean free path and the radial gradient lambda( parallel-to)G(r)BAR of galactic cosmic rays during three consecutive s olar cycles. The median rigidities of the primary particles being dete cted by the telescopes are 50 GV in the case of the surface muon teles cope and greater than 150 GV in the case of the underground muon teles copes. We have compared our results with those of a similar study made from observations of the solar diurnal variation by neutron monitors and an ion chamber, which have median rigidities of response between 1 7 and 70 GV (Bieber and Chen 1991a). The product lambda(parallel-to)G( r)BAR has a solar magnetic cycle dependence and our values axe lower t han those observed by neutron monitors, in agreement with the Bieber a nd Chen observation that lambda(parallel-to)G(r)BAR reverses after a s olar magnetic field reversal, in accordance with drift theories.