  The time-dependent modulation of galactic cosmic rays in the heliosphere is
studied by computing intensities using a time-dependent modulation model. By
introducing recent theoretical advances in the transport coefficients in the
model, computed intensities are compared with Voyager 1, International
Monitoring Platform (IMP) 8, and Ulysses proton observations in search of
compatibility. The effect of different modulation parameters on computed
intensities is also illustrated. It is shown that this approach produces, on a
global scale, realistic cosmic-ray proton intensities along the Voyager 1
spacecraft trajectory and at Earth upto ~2004, whereafter the computed
intensities recovers much slower towards solar minimum than observed in the
inner heliosphere. A modified time dependence in the diffusion coefficients is
proposed to improve compatibility with the observations at Earth after ~2004.
This modified time dependence led to an improved compatibility between computed
intensities and the observations along the Voyager 1 trajectory and at Earth
even after ~2004. An interesting result is that the cosmic-ray modulation
during the present polarity cycle is not determined only by changes in the
drift coefficient and tilt angle of the wavy current sheet, but is also largely
dependent on changes in the diffusion coefficients.
