DOPPLER SHIFT CORRELATIONS IN THE SOLAR TRANSITION REGION

摘要

I investigate dynamical correlations between the lower transition region and the upper transition region using spectra from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The measured quantity is the Doppler shift (mostly solar radial) along the line of sight. The purpose is to shed light on the fraction of the lower transition region that resides in cool structures not physically associated with higher temperature regions and the fraction that can be described by a classical transition region with a physical connection from the chromosphere into the corona. "Transition region" in this context means the transition region sufficiently bright in ultraviolet spectral lines to be observed. I find strong Doppler shift correlations between two different lower region lines from C Ⅳ and S Ⅴ, but much weaker correlations between these lines and a line of Ne Ⅷ formed well into the upper transition region. I conclude that most of the lower transition region that is observable because of its brightness arises in cool loop structures. The results also favor a scenario in which the lower transition region is heated and cooled transiently on timescales less than or perhaps comparable to the SUMER exposure times of 21 s for the data analyzed in this work.