Observations of the velocity distribution of solar wind ions

Abstract

Measurements made by the Isee 3 ion composition experiment have been used to determine the kinetic temperatures of 3 He ++ , 4 He ++ , 16 O 6+ , and 16 O 7+ in the solar wind. It is found that these temperatures generally obey the relation that T i /m i = const, but fluctuations, some of which are caused by dynamical effects in the flow, are observed. Whether this relation applies to ions with masses greater than 16 requires more analysis to determine. The temperature of oxygen sometimes rises above 10 6 °K, which is very strong evidence for heating outside the collisional region of the corona. The tendency toward equal temperatures per nucleon occurs everywhere where collisions are unimportant, suggesting that the temperatures are set up close to the sun rather than elsewhere in the interplanetary medium. The velocity distribution function of helium is observed to be non‐Maxwellian, with a pronounced high velocity tail. As this is one condition for heating by wave dissipation, this mechanism must still be considered as a heating mechanism.