DETECTION AND PARAMETERIZATION OF VARIATIONS IN SOLAR MID-ULTRAVIOLETAND NEAR-ULTRAVIOLET RADIATION (200-400 NM)

Nimbus 7 and Solar Stellar Irradiance Comparison Experiment (SOLSTICE) spacecraft measurements of solar irradiance both exhibit variability at mid (200-300 nm) and near (309-400 nm) ultraviolet (UV) wavelengths that are attributable to the Sun's 27-day solar rotation, even though instrument sensitivity drifts obscure longer-term, 11-year cycle vari ations, Competing influences of dark sunspots and bright faculae are t he dominant causes of this rotational modulation, Parameterizations of these influences using a newly developed UV sunspot darkening index a nd the Mg index facular proxy replicate the rotational modulation dete cted in both the broadband Nimbus 7 filter data (275-360 nm and 300-41 0 nm) and in SOLSTICE l-nm spectra from 200 to 400 nm. Assuming that t hese rotational modulation influences scale linearly over the solar cy cle, long-term databases of sunspot and global facular proxies permit estimation of Ii-year cycle amplitudes of the mid-and near-UV solar sp ectrum, unmeasured at wavelengths longward of 300 nm because of insuff icient long-term repeatability (relative accuracy) of state-of-the-art solar radiometers at these wavelengths. Reconstructions of UV irradia nces throughout the Ii-year solar cycle indicate variabilities of 0.17 3 W/m(2) (1.1%) in the integrated radiation from 200 to 300 nm and 0.2 4 W/m(2) (0.25%) in radiation from 300 to 400 nm, These two UV bands t hus contribute about 13% and 18%, respectively, to the 1.54 W/m(2) (0. 1%) total (spectrally integrated) radiative output solar cycle. The pa rameterizations allow customization of UV irradiance time series for s pecific wavelength bands required as inputs to general circulation mod el simulations of solar cycle forcing of global climate change, and ha ve practical implications regarding the long-term repeatability requir ed for future solar monitoring.