Voyager Plasma Wave Observations in the Very Local Interstellar Medium

Voyager plasma wave observations have provided the first in situ electron densities in the Very Local Interstellar Medium (VLISM) and evidence of effects of solar transients in this region just beyond the heliopause. These measurements reveal a large-scale radial density gradient in a boundary layer extending ~10 AU beyond the heliopause in the general direction of the heliospheric nose. Beyond the boundary layer is an extensive region with generally increasing electron densities to ~155 AU that are dominated by jumps from shocks and pressure fronts presumably originating in solar transients. We examine the occurrence of shocks as identified by electron plasma oscillation events as a function of radial distance and solar cycle. While it is reasonable to assume these effects decrease in occurrence frequency and/or amplitude as a function of distance due to dissipation, it is also the case that transient events are related to the solar cycle and that this may be as important or perhaps an even more important factor in the probability of detecting shock-related effects by the Voyager spacecraft.