  Observationally, it is difficult to establish at what rigidity the modulation
of galactic cosmic rays (CRs) actually begins in the heliosphere. It should be
possible to do if the relevant local interstellar CR spectra were known and
reliable measurements were made between 10 GV and about 200 GV, inside and
outside the heliosphere. Numerical models for solar modulation studies are
based on simply assuming that CR modulation begins at a given spatial boundary
and at rigidities between 30 to 50 GV, usually handled as an initial condition.
The Stochastic Differential Equations approach to numerical modelling presents
the opportunity to determine the level of modulation from high to low
rigidities because an initial condition at a prescribed high rigidity is not
required. We present the results of such an approach and show the percentage
modulation of CR protons as a function of kinetic energy between 100 MeV and
250 GeV.
