Observations of the Variable Coronal Solar Wind, and its Implications for Solar Probe Plus and Solar Orbiter

Solar wind observations from Ulysses show polar solar regions at solar minimum to be uniform and non-structured. However, when analyzing LASCO C2 and STEREO SECCHI COR2 coronagraph images, and using UCSD-developed correlation-tracking techniques, we find the observed solar wind outflow during these periods is not a static well-ordered motion, but instead has highly-variable speed structures. These high-speed polar structures are associated with slightly brighter (and also patchy) coronal structures. When the high-speed patches are averaged with the slower surrounding corona, the solar wind acceleration with solar distance is observed consistently across the polar coronal hole regions. This change in speed with distance is also consistent with the outward flow speed observed in polar regions determined from mass flux considerations and known coronagraph polarization brightness. From this we conclude that Solar Probe Plus and Solar Orbiter will not only be able to measure these structures in situ as variable wind, but they may also be able to determine the key parameters associated with these structures and how these parameters (abundances and magnetic fields) are related to the solar wind acceleration that is observed remotely in coronagraph observations.