Abstract
Abstract Measurements of the intensities and profiles of the resonantly scattered hydrogen Lyman-alpha line at 1216 A have provided important insights on the physical conditions in the extended corona where the solar wind originates. Comparisons of measured kinetic temperatures with predictions of models suggest that there is proton heating and/or a nonthermal contribution to the motions of coronal protons between 1.5 and 4 solar radii. Comparisons of measured Lyman-alpha intensities with predictions of models provide evidence for subsonic flow for r ⊙ in a quiet region of the corona and two polar coronal holes observed near solar maximum. There is evidence for supersonic flow ( ∼ 200 km s −1 ) at r ≈ 2 R ⊙ in a large polar coronal hole observed in 1982. Future measurements of HI Lyman alpha and other coronal lines will greatly expand the quality and quantity of UV spectroscopic measurements of the extended corona.
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