An ionospheric plasma fluid transport model is used to investigate the effects of soft (<1 keV) electron precipitation on high-latitude F region/topside ionospheric O+ upflows. In this paper we present a systematic modeling study of ionospheric effects of varying soft-electron precipitation, focusing on the resulting upward O+ ion velocities and fluxes, as well as the elevated ion and electron temperatures, due to the precipitation. Recent satellite observations [Seo et al., 1997> suggest an inverse relationship between upward O+ fluxes and the characteristic energy of the precipitating electrons for the same energy flux level. The modeling results presented here show this inverse relationship explicitly. Our interpretation is that a declining characteristic energy at constant energy flux increases the number of precipitating electrons available to heat the thermal electrons, and thus enhances the thermal electron temperature and hence the ambipolar electric field for propelling the upward O+ flows. The modeled increase of the thermal electron temperature with enhanced auroral electron precipitation is also generally consistent with the Seo et al. [1997> topside ionospheric plasma measurements. In addition, the modeling results presented here illustrate characteristic temporal development responses, showing dramatic increases in velocity, Mach number, and flux values during the first 10--13 min after the precipitation is turned on. By ~1 hour after the initiation of a soft-electron precipitation event the ion upward velocities and fluxes approach nearly stable, asymptotic values. ¿ 1999 American Geophysical Union