Voyager Evidence for Large-Scale Structure in Plasma and Energetic Particle Behavior Beyond the Termination Shock

Voyager 1 crossed the termination shock at the end of 2004, more than a full solar cycle ago. Similarly, Voyager 2 crossed it and entered the heliosheath at the end of August, 2007, which was before the beginning of SC 24. Voyager 1 crossed the heliopause in August, 2012, when solar activity was high. Thus, at each spacecraft changing readings over time in the heliosheath could be due either to the increasing solar distance or to changing solar activity. Comparing energetic particle observations by the two spacecraft at corresponding distances shows cases for which distance is more important. In particular, at both spacecraft the spectral index of protons in the anomalous cosmic ray energy range shows corresponding variations with distance, despite the differing times and the great separation between the spacecraft, and so do ratios of electron count rates in differential energy bands. These comparisons provide insight into the expectation that Voyager 2 will soon cross the heliopause. Consideration of the large-scale spatial structure of moving flare-generated disturbances also provides insight into particle behaviour associated with the plasma wave events observed by Voyager 1 since it crossed the heliopause. We discuss a variety of observations of these phenomena from the heliosheath and the local interstellar medium and suggest a possibility for future simulations. (paper)