PLASMA NEAR THE HELIOSHEATH: OBSERVATIONS AND INTERPRETATIONS

Voyager 2 (V2) has observed heliosheath plasma since 2007 August. The plasma flux decreases by 25% before the termination shock (TS), then, as V2 moved into the heliosheath, the plasma density, temperature, and flux all decreased by an additional factor of 2. We suggest three effects combine to cause these decreases. (1) V2 moved into the lower-flux transition region between the low- and high-speed solar wind. This hypothesis is consistent with Ulysses observations of the transition location, explains the 25% decrease in solar wind flux observed before the TS crossing, and can reconcile discrepancies between the V2 and Voyager 1 heliosheath speeds and between the V2 speeds and model results. (2) The weaker source at the Sun. (3) The heliosheath plasma turning and flowing toward the heliotail.