High-resolution Imaging of the Solar Chromosphere/Corona Transition Region

Abstract

The properties of a previously unresolved extreme-ultraviolet (EUV) emission in solar active regions are examined using coordinated data sets from the Transition Region and Coronal Explorer (TRACE) satellite, the Michelson Doppler Imager on the Solar and Heliospheric Observatory satellite, the Soft X-Ray Telescope (SXT) on the Yohkoh satellite, and the ground-based Swedish Vacuum Solar Telescope (SVST) on La Palma. The emission appears most prominently in TRACE Fe IX/Fe X 171 Å images as a bright dynamic network surrounding dark inclusions on scales of 2-3 Mm, confined to layers approximately 1-3 Mm thick with base heights approximately 2-4 Mm above the photosphere. It is seen only above plage regions that underlie (3-5) × 10⁶ K coronal loops visible in SXT images. The bright EUV elements emit at temperatures of about 10⁶ K. Fine-scale motions and brightness variations of the emission occur on timescales of 1 minute or less. The dark inclusions correspond to jets of chromospheric plasma seen in simultaneous SVST filtergrams in the wings of Hα. The combined characteristics imply that we are at least partially resolving the structure and dynamics of the conductively heated upper transition region between the solar chromosphere and corona.