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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg
The EUV Imaging Telescope (EIT) on the SOHO provides the capability for multi-wavelength imaging of the corona in four spectral bands, centered at 171, 195, 284, and 304 Angstroms, using multilayer telescope technology. These bands encompass coronal temperatures from 1 MK to 2.5 MK as well as the upper chromosphere, at about 60,000 K. In particular, nearly simultaneous imaging in the 171 and 195 Angstrom bands, the former including major Fe IX and Fe X emission lines, the latter including a strong Fe XII line, provides a capability to infer the morphology and characteristics of the corona at temperatures of 1.0 - 1.7 MK. We have examined the corona in this temperature range over an active region observed from SOHO from May - September, 1996 and find that low-lying loops (below a density scale height of 75,000 km, characteristic of Fe X) vary little in brightness and temperature along their length. For features extending to greater heights, however, both brightness gradients and temperature gradients are observed. Preliminary analysis of the observations when the region was on the West limb on September 30 indicates a small positive temperature gradient of approximately 0.5 K/km in one loop system that extended above 100,000 km. On the other hand, a nearly radial feature extending to the edge of the EIT FOV was isothermal or had at most a slight negative temperature gradient. Such measurements may have application to the modeling of coronal loops and streamers and the processes of coronal heating and solar wind acceleration.
Program listing for Friday