Semiempirical models of the solar atmosphere. II. The quiet-sun low chromosphere at moderate resolution

We present a new, one-dimensional model of the solar atmosphere ( called SRPM 305) at moderate angular resolution (similar to 1 ''-2 ''). Key characteristics of the SRPM 305 model include (1) a minimum temperature of similar to 3800 K at a gas pressure of similar to 80 dyne cm(-2) and (2) a rapid temperature rise above the temperature-minimum layer that results in substantial overionization of most elements when compared with LTE calculations. The model calculations reproduce the similar to 4300 Kminimumbrightness temperature of the UV continuum (between 1400-1500 angstrom) observed by SUMER and the similar to 4400 K observed minimum radio-continuum brightness temperature ( between wavelengths 0.01 and 100mm). Neither the UV nor the radio continuum bear on the low-temperature minimum value because their broad intensity contribution functions cause the higher temperatures of the upper chromospheric layers to effectively hide the low minimum temperature region. The SRPM305 model reproduces the observed intensities of CO lines at 4.466 mu m, at both the disk center and near the limb, by using C and O abundances consistent with recent literature low values. The model also reproduces observed intensities of C I spectral lines at 5381 and 8337 angstrom, CH lines at about 4306 angstrom, the CN band head at 3883 angstrom, and the O I lines at 7772, 7774, and 7776 angstrom, respectively. Using the SRPM 305 model, we find no significant abundance variations between the photosphere and the low chromosphere. Consequently, the single-component model presented here matches several apparently contradictory observations and thereby resolves the controversy about the temperature minimum value.