  The sidereal anisotropy of galactic cosmic ray (GCR) intensity observed with
the Tibet Air Shower (AS) experiment still awaits theoretical interpretation.
The observed global feature of the anisotropy is well reproduced by a
superposition of the bi-directional and uni-directional flows (BDF and UDF,
respectively) of GCRs. If the orientation of the deduced BDF represents the
orientation of the local interstellar magnetic field (LISMF), as indicated by
best-fitting a model to the data, the UDF deviating from the BDF orientation
implies a significant contribution from the streaming perpendicular to the
LISMF. This perpendicular streaming is probably due to the drift anisotropy,
because the contribution from the perpendicular diffusion is expected to be
much smaller than the drift effect. The large amplitude deduced for the UDF
indicates a large spatial gradient of the GCR density. We suggest that such a
density gradient can be expected at the heliosphere sitting close to the
boundary of the Local Interstellar Cloud (LIC), if the LIC is expanding. The
spatial distribution of GCR density in the LIC reaches a stationary state
because of the balance between the inward cross-field diffusion and the
adiabatic cooling due to the expansion. We derive the steady-state distribution
of GCR density in the LIC based on radial transport of GCRs in a spherical LIC
expanding at a constant rate. By comparing the expected gradient with the
observation by Tibet experiment, we estimate the perpendicular diffusion
coefficient of multi-TeV GCRs in the local interstellar space.
