CORRELATION HEIGHTS OF THE SOURCES OF SOLAR ULTRAVIOLET EMISSION LINES IN A QUIET-SUN REGION

摘要

The radiance and Doppler-velocity maps of the emission lines of Si Ⅱ, C Ⅳ, and Ne Ⅷ obtained in a quiet region of the Sun by SUMER (Solar Ultraviolet Measurements of Emitted Radiation) are correlated with the vertical component, B_z, of the magnetic field vector as extrapolated, by means of a force-free field model, from the photospheric magnetic field measured by MDI (Michelson Doppler Imager). It is found that, with increasing vertical height, each of the correlation coefficients initially increases to a maximum value before it decreases again. The height corresponding to this maximum is called the correlation height. For the data sets selected from a quiet-Sun region, the correlation heights of Si Ⅱ and C Ⅳ are near 2 Mm, and for Ne Ⅷ near 4 Mm. At their correlation heights, the averaged square root of the radiance of the emission lines of Si Ⅱ and C Ⅳ, considered as a proxy of the plasma density, has a linear relationship with |B_z|. This result supports the empirical concept that the solar transition region is very thin and still affected by frozen-in convection. A way for improvement of such studies is also outlined.