Kinetic temperature ratios of O6+ and He2+: Observations from Wind/MASS and Ulysses/SWICS

We present results from a two spacecraft study of the ratio of O6+ and He2+ kinetic temperatures as a function of solar wind speed. Data from the Wind/MASS and Ulysses/SWICS instruments both indicate the O6+/He2+ kinetic temperature ratio increases with increasing solar wind speed, peaking near 500 km/s. Above 500 km/s, the ratio appears to decrease slightly. Values near unity were obtained for slow solar wind while fast wind yielded ratios substantially higher than what is expected from the general rule T-i/T-j approximate to M(i)/M(j). (1) Although averaging over all data would result in the nominal ratio of 4, deviations from equation (1) appear to be common and the assumption of equal thermal velocities should not be made a priori.