New models of the solar chromosphere and transition region determined from SUMER observations

The SUMER atlas of Curdt et al.(2001) giving the solar disk-center spectrum between 67 and 161 nm, together with HRTS spectra to 173 nm, is an extremely valuable source of observational data that can be used to determine the structure of the upper photosphere, chromosphere, transition region, and low corona. The Pandora atmospheric modeling program is being used to determine atmospheric models and calculated spectra consistent with these observations, resulting in new models of the solar atmosphere in much better agreement with observations than before. We find that temperature variations of 400 K cause the computed chromospheric intensities to change by a factor of 4. This is greater than the intensity variations at chromospheric wavelengths 1) with time in quiet regions, and 2) with position from cell centers to bright network. These results appear to conflict with dynamical models that have time variations of 1000 K or more in the low chromosphere.