Observations of coronal structures above an active region by EIT and implications for coronal energy deposition

Solar EUV images recorded by the EW Imaging Telescope (EIT) on SOHO have be en used to evaluate temperature and density as a function of position in tw o largescale features in the corona observed in the temperature range of 1. 0-2.0 MK. Such observations permit estimates of longitudinal temperature gr adients (Lf present) in the corona and, consequently, estimates of thermal conduction and radiative losses as a function of position in the features. We examine two relatively cool features as recorded in EIT's Fe IX/X (171 A ngstrom) and Fe XII (195 Angstrom) bands in a decaying active region. The f irst is a long-lived loop-like feature with one leg, ending in the active r egion, much more prominent than one or more distant footpoints assumed to b e rooted in regions of weakly enhanced field. The other is a near-radial fe ature, observed at the West limb, which may be either the base of a very hi gh loop or the base of a helmet streamer We evaluate energy requirements to support a steady-state energy balance in these features and find in both i nstances that downward thermal conductive losses (at heights above the tran sition region) are inadequate to support local radiative losses, which are the predominant loss mechanism. The requirement that a coronal energy depos ition rate proportional to the square of the ambient electron density (or p ressure) is present in these cool coronal features provides an additional c onstraint on coronal heating mechanisms.