National Aeronautics and Space Administration

Living With A Star

Targeted Research and Technology

Solar UV Irradiance Variation during the Solar Cycle

ROSES ID: NRA-NNH04ZSS001N      Selection Year: 2005      

Program Element: Focused Science Topic

Principal Investigator: Linton E. Floyd

Affiliation(s): Interferometrics Inc.


Analysis of terrestrial climate data have shown effects of the solar activity cycle (e.g., Quasi Decadal Oscillation). Variations in the solar ultraviolet (UV) irradiance are one likely cause because of UV absorption in the Earth's various atmospheric layers. Recent climate simulations based on realistic models of atmopheric processes involving solar UV irradiance have shown that solar UV variation can cause significant terrestrial climate changes. Begun in 1978, space-based measurements of solar UV irradiance are often difficult to interpret because of uncertainties in the long-term responsivity calibration of the measuring instruments. Generally, the solar variations are large compared to these uncertainties for the shortest wavelengths (e.g. < 200 nm), but decline for longer wavelengths until ~300 nm where instrumental trends inevitably dominate. The goal of this research is to determine the solar cycle variation of the solar UV irradiance from the available data from several experiments. For each solar UV experiment and time period, the solar cycle variation will be determined. For wavelengths where the solar cycle can be observed directly, the solar cycle variation for rising or falling phases of the solar cycle will be directly calculated from the calibrated data. For longer wavelengths where instrumental trends dominate the solar variation, presence of the solar signal, as represented by the MgII core-to-wing ratio index and where possible the Photometric Sunspot Index, will be detected and the solar cycle variation inferred. The results will be interpreted in the context of and will be compared with the results of state-of-the-art synthetic solar spectum models.


Performance YearReferenceActions
1Floyd, L.; (2006), Measurements of Solar UV and EUV Irra...
1Floyd, L.; Herring, L.; (2006), Solar Cycle UV Irradia...
1Floyd, L.; Woods, T.; Deland, M.; (2007), Solar Cycle...
1Floyd, Linton; (2010), Measurements of Solar UV Irradianc...

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