Yohkoh soft X-ray determination of plasma parameters in a polar coronal hole

The Yohkoh Soft X-Ray Telescope (SXT) has been used to study the emission from a coronal hole surrounding the north pole of the Sun. Stronger emission from closed coronal structures in the line of sight can interfere with attempts to measure properties of coronal hole plasma. SXT observations indicate that the north polar region was free of such contamination on 1992 October 3. Measured X-ray intensities, corrected for background and scattered X-rays, are compared with a theoretical coronal hole model. They are found to be broadly consistent with the model predictions for variation of intensity with height and for limb brightening, although the electron density is lower than would be appropriate for model predictions based on solar maximum densities. Electron temperatures estimated by the filter ratio method are also consistent with the model and with an in situ estimate of the maximum electron temperature in the solar wind by the Ulysses ionic charge composition experiment.