Sources of the Solar Wind at Solar Activity Maximum

The photospheric sources of solar wind observed by the Ulysses and ACE spacecraft in 1998 to early 2001 are determined through a two-step mapping process. Solar wind speed measured at the spacecraft is used in a ballistic model to determine a footpoint on a source surface at a solar distance of 2.5 solar radii. A potential-field source-surface model is then used to trace the field and flow from the source surface to the photosphere. A detailed analysis is performed on four of the solar rotations for which the mapped and observed magnetic field polarities were in generally good agreement. For those rotations, the solar wind mapped to both coronal holes and active regions. These findings for a period of high solar activity differ from the findings of a similar study of the solar wind in 1994-5 when solar activity was very low. At solar minimum the fastest wind mapped to the interior of large polar coronal holes while slower wind mapped to the boundaries of those holes or to smaller low-latitude coronal holes. For the period of the present study, neither spacecraft detected wind from the small polar coronal holes when they existed. At solar minimum, field lines originating in polar regions bend equatorwards, whereas at solar maximum, field lines originating at mid-latitudes bend polewards. The principal difference between the solar wind from coronal holes and from active regions is that the O7+/O6+ ion ratio is lower for the coronal hole flow. The boundaries between plasma flows from neighboring sources are marked by large magnetic holes, plasma sheets, and low entropy, independent of whether the sources have the same or opposite magnetic polarities.