  An important factor limiting our ability to understand the production and
propagation of cosmic rays pertains to the effects of heliospheric forces,
commonly known as solar modulation. The solar wind is capable of generating
time and charge-dependent effects on the spectrum and intensity of low energy
($\lsim$ 10 GeV) cosmic rays reaching Earth. Previous analytic treatments of
solar modulation have utilized the force-field approximation, in which a simple
potential is adopted whose amplitude is selected to best fit the cosmic-ray
data taken over a given period of time. Making use of recently available
cosmic-ray data from the Voyager 1 spacecraft, along with measurements of the
heliospheric magnetic field and solar wind, we construct a time, charge and
rigidity-dependent model of solar modulation that can be directly compared to
data from a variety of cosmic-ray experiments. We provide a simple analytic
formula that can be easily utilized in a variety of applications, allowing us
to better predict the effects of solar modulation and reduce the number of free
parameters involved in cosmic ray propagation models.
