Spectra of the solar irradiance were obtained at the maximum and minimum of cycle 21 with the 1 m Fourier transform spectrometer at the McMath Telescope on Kitt Peak. Differences between these spectra are expressed as changes in absorption line blanketing. We compare these changes with total solar irradiance measured during the same period from space by ACRIM on SMM. Fraunhofer lines in the 500-560 nm range increased in depth and equivalent width as the ACRIM signal decreased from 1981 to 1987. An interpretation based on sunspots and faculae being added to the atmosphere at solar maximum can account for less than 4% of the ACRIM decrease to be arising in the 500-560 nm range. The data show that the ultraviolet, with its much greater line blanketing, is more important, in agreement with the findings of Lean. The major uncertainty in our simple modeling of the components of the irradiance spectrum-quiet photosphere, sunspots, and faculae-is the facular continuum contrast. Our blanketing analysis in the whole range 300-560 nm can account for only 32%-58% of the ACRIM measured change, depending on whether the facular continuum contrast is 1.00 or 1.02. An accounting of the solar irradiance variation, however, can be made complete by combining our results with those of Lean for the range 200-300 nm and ascribing to an unresolved facular-like active network a contrast a few percent higher than for the plage-related faculae. A cycle-dependent emission component of this kind is consistent with our measured blanketing changes as well as with the results of earlier investigations.
