  The long-term dynamics of Oort cloud comets are studied under the influence
of both the radial and the vertical components of the Galactic tidal field.
Sporadic dynamical perturbation processes are ignored, such as passing stars,
since we aim to study the influence of just the axisymmetric Galactic tidal
field on the cometary motion and how it changes in time. We use a model of the
Galaxy with a disc, bulge and dark halo, and a local disc density, and disc
scale length constrained to fit the best available observational constraints.
By integrating a few million of cometary orbits over 1 Gyr, we calculate the
time variable flux of Oort cloud comets that enter the inner Solar System, for
the cases of a constant Galactic tidal field, and a realistically varying tidal
field which is a function of the Sun's orbit. The applied method calculates the
evolution of the comets by using first-order averaged mean elements. We find
that the periodicity in the cometary flux is complicated and quasi-periodic.
The amplitude of the variations in the flux are of order 30%. The radial motion
of the Sun is the chief cause of this behaviour, and should be taken into
account when the Galactic influence on the Oort cloud comets is studied.
