On the outflow in an equatorial coronal hole

Abstract

We report new observations concerning the source of the fast solar wind by directly comparing Doppler-shift maps of Ne 7 + with charts of the photospheric magnetic field in an equatorial coronal hole, which was observed by SUMER/SOHO and NSO/Kitt Peak on November 5, 1999. The relationship between the velocity field, line intensity and magnetic network is discussed. Our data show that there are both dark and bright regions in this coronal hole as seen in the Ne VIII line. The larger blue shifts of the Ne VIII line are associated mainly with the darker region, where the strong magnetic flux with a single polarity is concentrated. Conversely, the smaller blue shifts are measured mainly in the brighter region, with an underlying mixed-polarity magnetic structure. These observational results are in agreement with the model prediction that the fast solar wind is initially accelerated in the coronal funnels, which are regions with globally open coronal fields rooted in the magnetic network.