The Three-Dimensional Structure of the Solar Wind over the Solar Cycle

Throughout declining and minimum phases of the solar cycle the solar wind displays a simple global structure with fast, tenuous flows emanating from large polar coronal holes filling the interplanetary medium at mid and high latitudes, and slower, denser, and much more variable flows at low latitudes. Approaching solar maximum a complicated mixture of flows from streamers, small coronal holes, and coronal mass ejections extends to higher and higher heliolatitudes, ultimately covering even the poles as the polar coronal holes shrink, fragment, and disappear. The most recent observations have continued through solar cycle 23 maximum with the formation of a mid-sized, circumpolar coronal hole in the northern hemisphere. By April of 2002, Ulysses had again moved back down to ∼45° N, however, this hole has not yet grown to nearly the size of those observed in the previous orbit nor pushed fast solar wind down to mid-latitudes. Rather, a complex mixture of solar wind flows is observed below ∼70° N in these recent observations. This interval also provided a unique geometry where Ulysses skimmed along, nearly parallel to the boundary of the polar coronal hole over several solar rotations. These times contain substantial intermediate speed solar wind, supporting the previous findings of McComas et al. [2002a] of thin boundary layers (CHBLs) flanking coronal holes.