LIMITS ON DECELERATION AND ASYMMETRY OF SOLAR-WIND SPEED

It has been suggested by Richardson et al. [1995] that the solar wind shows signs of deceleration due to mass-loading by interstellar pickup ions. They based their conclusion on observations from the Voyager 2 and IMP 8 spacecraft. Observations from the Pioneer Venus Orbiter (PVO), IMP 8, Voyager 2, and Pioneer 10 spacecraft are compared to look for this deceleration. While these comparisons suggest the possibility of deceleration at Voyager 2, the magnitude of this deceleration appears to be significantly less than the deceleration reported by Richardson et al. [1995]. Some of this difference could be explained by a north-south asymmetry in solar wind speed during solar cycle 21. The implications of these results are discussed, along with possibilities for further investigations.