Sergey Marchenko & M. DeLand - 613 Seminar Series

Understanding the temporal and spectral variability of solar irradiance is a crucial element in determining the Earth's energy balance, thus Earth's climate. Assessment of solar variability with satellite measurements on multi-year time scales has proven to be difficult, due to the complex changes in instrument response after launch. The excellent stability of the Ozone Monitoring Instrument (OMI) on the Aura satellite allows us to reveal and monitor both short-term (solar rotation) and long-term (solar cycle) changes of the spectral solar irradiance (SSI) between 265-500 nm during the current Cycle 24, from 2009 to the present. SSI variability in the relatively line-free regions amounts to ~0.6% ± 0.2% around 265 nm, gradually diminishing to 0.15%± 0.20% at 500 nm. All strong spectral lines and blends, with a notable exception of upper-Balmer lines, vary in unison with the solar 'continuum'. Besides the well-known lines with a strong chromospheric component (Mg II, Ca II), the most involved species include Fe I blends and all prominent CH, NH and CN molecular bands. Following the general trend seen in the solar 'continuum', variability of spectral lines also decreases toward longer wavelengths. We demonstrate that in the 265-500nm range the magnitude and spectral dependence of short-term and long-term SSI changes are consistent to within derived uncertainties. The OMI data on the short-term SSI variability agree with concurrent results from the GOME-2 instrument on the ESA MetOp satellite, and with observations from previous solar cycles. OMI long-term solar variations agree with the NRLSSI model predictions, but disagree with variations determined from SORCE SIM and SOLSTICE solar measurements.