The magnetic connectivity of moss regions

A novel emission feature resembling moss was first identified in high-resolution TRACE Fe IX/X 171 Å images by Berger et al. (1999). The moss emission is characterized by dynamic arc-second scale, bright elements surrounding dark inclusions in images of solar active regions. Patches of moss elements, called moss regions, have a scale of 20-30 Mm. Moss regions occur only above some of magnetic plages that underlie soft X-ray coronal loops. Using the potential field extrapolation of the photospheric magnetic field into the corona, we find that the magnetic field lines in moss-associated magnetic plages connect with adjacent plages with opposite polarity; however, all field lines from mossless plages end in surrounding 'quiet regions'. This result is consistent with the idea that the TRACE moss is the emission from the upper transition region due to heating of low-lying plasma by field-aligned thermal conduction from overlying hot plasma (Berger et al., 1999).