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abstract
The variability of the solar full disk flux in the 1175-2100 \AA\ wavelength range is largely determined from the surface distribution on the Sun of active regions, whose increase and decrease over the solar cycle, and passage across the disk, is the main source of long term, and 27 day, variability. Variations in the distribution of brightness in quiet areas, perhaps from decay of active regions causing an enhanced network (``third component"), could also affect variability. While earlier models of the full disk variability have relied on proxy activity indicators, such as the Ca II plage area, a more direct indicator of activity may be full disk photospheric magnetograms. We have recast our earlier model (1980, J.G.R., 85, 2257) of ultraviolet variability to base it upon Kitt Peak full disk magnetograms, using the work of Cook and Ewing (1990, Ap. J., 355, 719) on the observed relationship of brightness at 1600 \AA\ with magnetic field strength. We compare our model results with observations of the solar irradiance from the SUSIM experiment flown on the UARS satellite.
