We discuss two extraordinary increases of cosmic ray intensity observed by Voyager 1 in the last 1.1 AU before heliopause crossing, Aug 2012 at 121.7 AU. The two increases are roughly similar in amplitude and result in a total increase of cosmic ray
nuclei around 1 GV of over 50 percent and of 0.01 GV electrons of a factor about 2. During the first increase, the changes in the magnetic, B, field are small. After the first increase, the B field variations and cosmic ray changes become large and during the second increase the B field variations and the cosmic ray changes are correlated to within a day. The intensity variations of H and He nuclei during these time intervals are measured from 0.1 to over 1 GV. The total GCR increse over the two events resemble those expected from a simple force-field like solar modulation model with a modulation potential of about 80MV. This is nearly one third of the total modulation potential of about 250 GV required to produce the modulation of these particles observed at the earth at the 2009 sunspot minimum and adds a new aspect to ideas about heliospheric 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 galacti
c 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.
Voyager 1 has explored the solar wind-interstellar medium interaction region between the Terminal Shock and the Heliopause, following the intensity distribution of the shock accelerated anomalous component of cosmic rays in the MeV energy range. The
sudden disappearance of this component at 121.7 AU from the sun is discussed in terms of three models for the transition into the interstellar plasma flow. Particles trapped flowing parallel to the boundary may penetrate up to one Larmour radius beyond. If the boundary is stationary, Voyager 1 directly samples this distance. The boundary could flap, depending on Heliosheath pressure changes and Voyager 1 then samples the extent of this motion. Finally, a turbulent boundary layer is considered in which the MeV particle distribution falls off with distance, thus measuring diffusion within the layer.
