Correlation Height of the Emission Source of Si Ⅱ in a Coronal Hole Region

The height of the source for Si Ⅱ represents the altitude of the bottom of the solar transition region. It is a new method to determine the so-called correlation height, by correlating the radiance of the FUV/EUV line with the magnetic field from a force-free extrapolation, as the height of the FUV/EUV emission source. A previous study found that the height of the source for SiⅡdetermined by applying this method in a coronal hole region is higher than that in the traditional view, which is so limited that it requires more data analysis to check. Using this method, the radiance data of SiⅡ, obtained in a south coronal hole region of the Sun by SOHO/SUMER, and the photospheric magnetic field, measured by NSO/KP （National Solar Observatory/Kitt Peak）, were analyzed. And the correlation height of SiⅡ is determined to be about 5.0 Mm for the data sets selected from a south coronal hole region. This result supports the recent conclusion that the bottom of the transition region in the coronal hole region is quite higher than that in the quiet-Sun region. Besides, a little difference from the previous study is found and the reason for this is speculated.