Transient Heliosheath Modulation
  Voyager 1 has explored the solar wind-interstellar medium interaction region
between the terminal shock and heliopause following the intensity distribution
of galactic cosmic ray protons above 200 MeV energy. Before this component
reached the galactic level at 121.7 AU, 4 episodes of rapid intensity change
occured similar to the Forbush Decreases found near the sun, rather than the
expected result of models related to those describing Long Term Modulation in
the inner solar system. Because the mean solar wind flow is both expected and
observed to be perpendicular to the radial direction close to the heliopause,
explanation is given in terms of transient radial flows related to possible
heliopause boundary flapping. It is necessary that radial flows are at the
sound speed found for conditions downstream of the teminal shock and that the
relevant perpendicular cosmic ray diffusion is controlled by 'slab' field
fluctuations accounting for 20 percent or less of the total power in field
variance. However, additional radial drift motion related to possible north to
south gradients in the magnetic field may allow the inclusion of some diffusion
according to 2-D turbulence theory. The required field gradients may arise due
to variation in the field carried by the solar plasma deflected away from the
solar equatorial plane. Modulation amounting to a total 30 percent drop in
galactic intensity requires explanation by a combination of several transient
episodes.
