Identification of the coronal sources of the fast solar wind

The present spectroscopic study of the ultraviolet coronal emission in a polar hole, detected on 1996 April 6-9 with the Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory spacecraft, identifies the interplume lanes and background coronal hole regions as the channels in which the fast solar wind is preferentially accelerated. In interplume lanes, at heliocentric distance 1.7 R., the corona expands at a rate between 105 and 150 km s(-1), that is, much faster than in plumes in which the outflow velocity is between 0 and 65 km s(-1). The wind velocity is inferred from the Doppler dimming of the O VI lambda lambda 1032, 1037 lines, within a range of values, whose lower and upper limit corresponds to anisotropic and isotropic velocity distribution of the oxygen coronal ions, respectively.