Solar spectral irradiance

During solar Cycle 24, in the relatively line-free regions the SSI changed by ~0.6%+/-0.2% around 265 nm. These changes gradually diminish to 0.15%+/-0.20% at 500 nm.

All strong spectral lines and blends, with the notable exception of the upper Balmer lines, vary in unison with the solar "continuum." Besides the lines with strong chromospheric components, the most involved species include Fe I blends and all prominent CH, NH, and CN spectral bands. Following the general trend seen in the solar "continuum," the variability of spectral lines also decreases toward longer wavelengths. The long-term solar cycle SSI changes are closely, to within the quoted 0.1%-0.2% uncertainties, matched by the appropriately adjusted short-term SSI variations derived from the 27 day rotational modulation cycles.