Abstract
Spartan 201 is a small shuttle-launched and -retrieved satellite, whose mission is to study the origins of the solar wind. It carries on board two instruments, the Ultraviolet Coronal Spectrometer and the White-Light Coronagraph. The third mission of the Spartan 201 (1995 September 7-10) spacecraft was to provide a solar context for the in situ particles and fields measurements during the north polar passage of the Ulysses spacecraft. In this Letter, we characterize the physical conditions of the north polar coronal hole as derived from white-light coronal observations by the Spartan 201-03 White-Light Coronagraph, the ground-based K coronameter in Mauna Loa, Hawaii, and Ulysses observations of in situ particles and their velocity. For the first time, we are able to combine in situ and path-integrated measurements in a coronal hole, to yield a consistent electron density (N) profile from the Sun to the Earth and the outer heliosphere. By using the value of N measured by Ulysses (1.8-4 AU), we are able to determine the actual value of N and not just an upper limit in the polar coronal hole, near the Sun. The current N profile suggests that the acceleration of the fast solar wind in a coronal hole is complete by 10-15 R, much closer to the Sun than had been previously expected.
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