Ulysses observations of differential alpha-proton streaming in the solar wind

Details Ulysses observations of differential alpha-proton streaming in the solar wind Ulysses observations of differential alpha-proton streaming in the solar wind

Aug 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996jgr...10117047n&link_type=abstract

Journal of Geophysical Research, Volume 101, Issue A8, p. 17047-17056

Physics

40

Interplanetary Physics: Solar Wind Plasma, Interplanetary Physics: Mhd Waves And Turbulence, Interplanetary Physics: Plasma Waves And Turbulence, Interplanetary Physics: Sources Of The Solar Wind

Scientific paper

Data from the solar wind spectrometer on the Ulysses spacecraft are used 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° to +/-80° during the period December 1990 through September 1995. The study is based on 6-hour averages of the parameter Vαp=|Vα-Vp| where Vα and Vp are the vector velocities of the alpha particles and protons, respectively. It is found that Vαp decreases with increasing distance 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 Vαp declining, on the average, as T-0.70+/-0.07. After normalization by this travel time factor, there is no residual dependence of Vαp on heliographic latitude thus ruling out any rotational effects on either the acceleration or deceleration of the alphas relative to the protons. There is also no significant difference in the normalized values of Vαp between quasi-stationary and transient (coronal mass ejection) flows. The ratios Vαp/VA, where VA is the Alfvén speed, and Vαp/Vwave, where Vwave is the observed propagation speed of Alfvénic fluctuations, both decline with increasing distance from the Sun, but Vαp/Vwave 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 Vαp and the amplitudes of fluctuations in both the magnitude and the direction of the interplanetary magnetic field. Although Vαp anticorrelates strongly with the ratio of the Coulomb collision time to the solar wind expansion time, it is believed that the correlation is not evidence of a cause and effect relation between those two parameters over much of the solar wind regime observed by Ulysses. Where comparisons are possible, the Ulysses data closely agree with extrapolations of the Helios data to greater solar distances.

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