  We deduce on hourly basis the spatial gradient of the cosmic ray density in
three dimensions from the directional anisotropy of high-energy (~50 GeV)
galactic cosmic ray (GCR) intensity observed with a global network of muon
detectors on the Earth's surface. By analyzing the average features of the
gradient in the corotational interaction regions (CIRs) recorded in successive
two solar activity minimum periods, we find that the observed latitudinal
gradient (Gz) changes its sign from negative to positive on the Earth's
heliospheric current sheet (HCS) crossing from the northern to the southern
hemisphere in A<0 epoch, while it changes from positive to negative in A>0
epoch. This is in accordance with the drift prediction. We also find a negative
enhancement in Gx after the HCS crossing in both A<0 and A>0 epochs, but not in
Gy. This asymmetrical feature of Gx and Gy indicates significant contributions
from the parallel and perpendicular diffusions to the the gradient in CIRs in
addition to the contribution from the drift effect.
