Line-blanketing variations in the irradiance spectrum of the sun from maximum to minimum of the solar cycle

Solar irradiance spectra obtained at or near the maximum and minimum phases of the solar magnetic activity cycle are compared. The characteristics of these spectra are related to the irradiance measurements available from the Active Cavity Radiometer Irradiance Monitor (ACRIM) of the SMM. An interpretation based on sunspots and faculae being added to the atmosphere at solar maximum can account for less than 4 percent of the ACRIM decrease to be arising in the 500-560 nm range. The UV, with its much greater line-blanketing, is more important, in agreement with the finding of Lean (1989).