The spatial correlation of the non-thermal velocities for O IV and Si IV in the lower transition region Original Research Article

We analyze the spatial relationship between non-thermal velocities derived from spectral lines of O IV. λ1401.16 (1.6×105 K) and Si IV λ1402.77 (6.3x104 K) in the solar lower transition region. The lines formed at different temperatures are observed simultaneously and at the same locations on the solar disk by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on board the Solar and Heliospheric Observatory (SOHO). In order to improve the accuracy of the non-thermal velocities determined from the full width at half maximum (FVJHM) intensities of the lines, we select data with sufficient counting statistics such that the uncertainty of the non-thermal velocity is less than 10 % of its value derived from the FWHMs. The spatial relationship between lines of O IV and Si IV shows a strong correlation. The correlation coefficient of the turbulent velocity is 0.856 for bright quiet Sun regions.