Ulysses Transition into the Polar Coronal Holes

Details Ulysses Transition into the Polar Coronal Holes Ulysses Transition into the Polar Coronal Holes

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh14a1700v&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SH14A-1700

Physics

2164 Solar Wind Plasma, 2169 Solar Wind Sources, 7511 Coronal Holes

Scientific paper

The Ulysses spacecraft has now half-completed its third polar orbit around the Sun. Like the first polar orbit, in 1992-1998, it is occurring at declining to minimum solar activity. Yet the two transitions into the hole are remarkably different. The first transition was substantially more regular than the second one is. This may be understood in the context of the current sheet orientation, which was generally flatter during the first transition, but is more strongly warped during the second. We model the global distribution of slow and fast solar wind streams starting from the Wilcox Solar Observatory maps of the solar magnetic field at the source surface. The model assumes slow solar wind to emanate from the vicinity of the current sheet with a speed that increases as a function of angular distance from the CS, i.e., with magnetic latitude, as it has been found on Helios. Fast solar wind of constant speed is assumed to emanate from the coronal holes and to expand superradially so as to fill the entire solid angle above a certain magnetic latitude. Thus we obtain a model solar wind speed at the position of Ulysses, and comparing to the observed solar wind speed there we can optimize the model to finally obtain the angular width of the belt of slow solar wind around the heliospheric current sheet.

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