ULYSSES OBSERVATIONS OF DIFFERENTIAL ALPHA-PROTON STREAMING IN THE SOLAR-WIND

Data from the solar wind spectrometer on the Ulysses spacecraft are us ed to study the differential streaming between the alpha particles and protons in the solar wind over the heliographic distance range of 1.3 to 5.4 AU and latitudes from 0 degrees to +/- 80 degrees during the p eriod December 1990 through September 1995. The study is based on 6-ho ur averages of the parameter V-alpha p = \V-alpha - V-p\ where V-alpha and V-p are the vector velocities of the alpha particles and protons, respectively. it is found that V-alpha p decreases with increasing di stance from the Sun and with decreasing solar wind speed. The distance and velocity dependencies can be combined into a single dependence on travel time T from the Sun to the point of observation, with V-alpha p declining, on the average, as T--0.70+/-0.07. After normalization by this travel time factor, there is no residual dependence of V-alpha p on heliographic latitude thus ruling out any rotational effects on ei ther the acceleration or deceleration of the alphas relative to the pr otons. There is also no significant difference in the normalized value s of V-alpha p between quasi-stationary and transient (coronal mass ej ection) flows. The ratios V-alpha p/V-wave where V-A is the Alfven spe ed, and V-alpha p/V-wave, where V-wave is the observed propagation spe ed of Alfvenic fluctuations, both decline with increasing distance fro m the Sun, but V-alpha p/V-wave remains in the range of 1.0 to 1.5 out to a travel time of 5 or 10 days. There are weak correlations between the normalized value of V-alpha p and the amplitudes of fluctuations in both the magnitude and the direction of the interplanetary magnetic field. Although V-alpha p anticorrelates strongly with the ratio of t he Coulomb collision time to the solar wind expansion time, it is beli eved that the correlation is not evidence of a cause and effect relati on between those two parameters over much of the solar wind regime obs erved by Ulysses. Where comparisons are possible, the Ulysses data clo sely agree with extrapolations of the Helios data to greater solar dis tances.