From a refined analysis of 4 years of data of the ion composition instrument on board ISEE 3 we find that in the overwhelming majority of observations kinetic temperatures of ions are approximately proportional to their masses. The logarithmic average for T(4He++) is 5.363; for T(O6+) and T(O7+) it is 5.978 and 6.000, respectively, corresponding to T(O)/T(He)=4.2. For ⟨log T(Fe)⟩ we find 6.52, corresponding to T(Fe)/T(He)=14. The correlation coefficients between oxygen and helium kinetic temperatures are high (~0.78 or above), whereas for the correlation log T(Fe) versus log T(He) we find a value of only 0.44 due to the large measurement uncertainties of T(He). Significant deviations from the mass/temperature proportionality are found at occasions of cool and dense solar wind flow when Coulomb collisions succeed to equilibrate kinetic temperatures of different ions species. |