Observations of the interplanetary medium: Vela 3 and Imp 3, 1965-1967

Simultaneous observations were made of the interplanetary plasma by the Vela 3 satellites and of the interplanetary magnetic field by the Imp 3 satellite from July 1965 to July 1967. Certain derived plasma properties are computed and statistically summarized. The quiet solar wind, defined by the velocity range 300≤V≤350 km/sec, is found to be represented by an average field strength of 4.7 γ at ϕSE=137° (317°), θSE=−3.2°, but having significant temporal departures from these averages. The ratio of plasma ion thermal energy density to magnetic-field energy density averages 1.2, with an average βp of 0.78. The average Alfvén speed is derived to be 36 km/sec, which yields a Mach number flow for the solar wind of 10.7. The solar-wind plasma most often is stable with respect to the firehose mode of instability. A nonstationary sector pattern does not destroy the sequence of correlated variations of plasma and field parameters observed within the sectors, although the distortion of sectors by propagating shock waves is suggested.