  Drifts in the Parker spiral interplanetary magnetic field are known to be an
important component in the propagation of galactic cosmic rays, while they are
thought to be negligible for Solar Energetic Particles (SEPs). As a result they
have so far been ignored in SEP propagation modelling and data analysis. We
examine drift velocities in the Parker spiral within single particle
first-order adiabatic theory, in a local coordinate system with an axis
parallel to the magnetic field. We show that, in the presence of scattering in
interplanetary space, protons at the high end of the SEP energy range
experience significant gradient and curvature drift. In the scatter-free case,
drift due to magnetic field curvature is present. The magnitude of drift
velocity increases by more than an order of magnitude at high heliographic
latitudes compared to near the ecliptic; it has a strong dependence on radial
distance r from the Sun, reaching a maximum at r~1 AU at low heliolatitudes and
r~10 AU at high heliolatitudes. Due to the mass over charge dependence of drift
velocities, the effect of drift for partially ionised SEP heavy ions is
stronger than for protons. Drift is therefore likely to be a considerable
source of cross field transport for high energy SEPs.
