Radial evolution of the solar wind speed as one source of alpha to proton ratio variations

The relative abundance of alphas to protons in the solar wind varies with solar wind speed and on solar cycle time scales. However, the WSA-Enlil model shows significant stream interactions and solar wind velocity evolution within a few tenths of an AU of the sun, resulting in solar wind speeds observed at 1.0 AU and beyond which can be very different from those in the outer corona (tens of solar radii). Tracing back the in situ measurements from Wind and ACE during the years 1995-2007, through the inner heliosphere using the WSA-ENLIL model, we relate solar wind observations of speed and the relative alpha to proton abundance to properties of its source regions in the corona and photosphere (e.g. modeled coronal solar wind speed, magnetic flux tube expansion factor, foot point field strength and location). In particular we address the alpha to proton number density ratio variation with heliographic latitude which is present during the previous solar minimum, but absent during the current solar minimum.