On the latitudinal dependence of the alpha-particle density in the solar wind

Some aspects of the heliographic latitude variation of the alpha-particle abundance in the solar wind have been studied using Ulysses data. The relative alpha-particle abundance, namely referred to the proton content, is seen to change with latitude in relation to the different kinds of solar wind observed by the spacecraft along its trajectory. Here we focus on (1) the first mid-latitude phase of the mission, when the spacecraft intermittently enters the polar wind, and (2) the region around the perihelion, when low-latitude wind in conditions of low solar activity is observed. Specifically, while a positive correlation between the alpha-particle abundance and the solar wind velocity is observed in the second case, this does not hold for the first case. We suggest that this result may be indicative of a difference, between the two regions, in the slow wind generation processes.