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 fo r this deceleration. While these comparisons suggest the possibility o f deceleration at Voyager 2, the magnitude of this deceleration appear s to be significantly less than the deceleration reported by Richardso n et al. [1995]. Some of this difference could be explained by a north -south asymmetry in solar wind speed during solar cycle 21. The implic ations of these results are discussed, along with possibilities for fu rther investigations.