MAGNETIC SOURCES OF THE SOLAR IRRADIANCE CYCLE

Using recently processed Ca K filtergrams, recorded with a 1 Angstrom filter at the Big Bear Solar Observatory (BBSO), we quantitatively ass ess the component of solar irradiance variability attributable to brig ht magnetic features on the Sun's disk. The Ca K filtergrams, ''flatte ned'' by removing instrumental effects and center-to-limb variations, provide information about bright sources of irradiance variability ass ociated with magnetic activity in both active regions and dispersed ac tive region remnants broadly distributed in the supergranule network ( termed collectively ''faculae''). Procedures are developed to construc t both total and UV spectral solar irradiance variations explicitly fr om the processed Ca K filtergrams, independently of direct irradiance observations. The disk-integrated bolometric and UV facular brightness signals determined from the filtergrams between late 1991 and mid-199 5 are compared with concurrent solar irradiance measurements made by h igh-precision solar radiometers on the Upper Atmosphere Research Satel lite (UARS). The comparisons suggest that active-region and active-net work changes can account for the measured variations. This good agreem ent during a period covering most of the decline in solar activity fro m the cycle 22 maximum to the impending solar minimum directly implica tes magnetic features as the sources of the 11 yr irradiance cycle, ap parently obviating the need for an additional component other than spo ts or faculae.