Plasma Flows in the Heliosheath

The Voyager spacecraft provide the first opportunity to study in situ the physics of the plasma in the heliosheath, the region of the shocked solar wind between the termination shock and the heliopause. The plasma flow speed at Voyager 2 is faster than that observed at Voyager 1, an unexpected finding. Flow in the T direction (RTN coordinates) is larger than in the N direction. This may indicate that the termination shock is wider in the T than N directions, but there is an alternate interpretation involving heliosheath flow patterns diverging from the stagnation point. The N component of the flow oscillates with a 110-day period whereas the T component is fairly constant. We suggest that these oscillations are due to a change in the shock orientation in the RN plane, perhaps caused by latitudinal changes in the solar wind.