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L. Fletcher (Lockheed Martin Solar and Astrophysics Lab.), B. De Pontieu (Stanford-Lockheed Institute for Space Research)
Recent observations of solar active regions with the Transition Region And Coronal Explorer (TRACE) have revealed finely textured, low-lying extreme ultraviolet (EUV) emission, called the ``moss'', appearing as a bright dynamic pattern with dark inclusions. The moss has been interpreted as the upper transition region by Berger et al., (1999). In this study we use simultaneous SOHO Coronal Diagnostic Spectrometer (CDS) and TRACE observations of Active Region (AR) 8227 on 30-May-1998 to determine the physical parameters of the moss material. A differential emission measure (DEM) analysis and other diagnostic tools establish that the plasma responsible for the moss emission has a temperature range of 0.6-1.5 \cdot 106~K and is associated with hot loops (T > 2 \cdot 106~K) observed with CDS. This plasma has an electron density of 2-5\cdot 109~{\rm cm}-3 at a temperature of 1.3 \cdot 106~K, giving a pressure of 0.7-1.7 dyne~cm-2. Both the density and pressure in the moss plasma are a few times higher than in coronal loops observed in the TRACE Fe IX/X 171~Å~passband. The volume filling factor of the moss plasma is of the order 0.1 and the path along which the emission originates is of the order 1,000 km long.
If the author provided an email address or URL for general inquiries,
it is as follows:
http://blackadder.lmsal.com/~bdp/mosslett_sub.ps