Comparison of empirical models for polar and equatorial coronal holes

We present a self-consistent empirical model for several plasma parameters of a large equatorial coronal hole observed on 1999 November 12 near solar maximum. The model was derived from observations with the Ultraviolet Coron agraph Spectrometer on the Solar and Heliospheric Observatory. In this Lett er, we compare the observations of O VI lambda lambda 1032, 1037 emission l ines with previous observations of a polar coronal hole observed near solar minimum. At the time of the 1999 observations, there was no evidence of la rge polar coronal holes. The resulting empirical model for the equatorial c oronal hole describes the outflow velocities and most probable speeds for O 5+, and we compared the derived ion properties with the empirical model for a solar minimum polar coronal hole. The comparison of the empirical models shows that the 1999 equatorial hole has lower O5+ outflow speeds and perpe ndicular temperatures than its polar counterpart from 1996 to 1997 at heigh ts between 2 and 3 R.. However, in situ asymptotic speeds of the wind strea ms coming from the 1996-1997 polar hole and from the 1999 equatorial hole a re only similar to 15% different. Thus, the bulk of the solar wind accelera tion must occur above 3 R. for the equatorial coronal hole. The equatorial hole also has a higher density than the polar hole at similar heights. It i s not yet known whether the higher densities are responsible for the seemin g inhibition of the fast ion outflow speeds and extremely large perpendicul ar temperatures that occur in polar coronal holes at solar minimum. We disc uss the constraints and implications on various theoretical models of coron al heating and acceleration.