Differential Flow Speeds of Ions of the Same Element: Effects on Solar Wind Ionization Fractions

Abstract

In previous studies of solar wind ion fractions it has always been assumed that ions of the same element flow with the same flow speed. In the present paper, we investigate the effects of differential flow speeds between different ionization states of the same element on the formation of O, C, Mg, Si, and Fe ions. We show that if the difference in flow speeds of adjacent ions, vi and vi+1, is large, the discrepancy between observed in situ ion fractions and low coronal electron temperature can be significantly reduced. The calculations are carried out for a radial profile of the electron temperature chosen in agreement with Solar Ultraviolet Measurement of Emitted Radiation (SUMER) measurements of coronal dark lanes and with two radial profiles of the electron density representing lower and upper observational limits. In order for the differential flow speeds to close the gap between the ion fractions observed in situ and the ones predicted from the low electron temperature observed in the corona, the differential flow speeds have to be extremely large in the regions where the ions are formed, e.g., below 1.5RS for O ions and below 2.5RS for Si ions; and in the case of Si, the coronal electron density has to be at the upper limit of observed values. In the cases of C, O, Mg, and Fe, the lower limit on the electron density is also acceptable.