Distribution of radial and tangential speeds for the solar wind protons and alpha particles. All the E03 and E04 observations of the proton core (vertical ticks) and alpha particles (plus signs) from SPAN-Ion are plotted in the left panel in grey, with the fast (F1 and F2) and slow (S1 and S2) wind streams highlighted. The distributions from the fast and slow wind streams are shown separately in the middle and right panels, respectively. These include the proton beam (crosses) for completeness. In each case, the average difference vector between the alpha particle and proton core velocities in the RT-plane are annotated (shifted away from the data).