The role of solar variability in climate change
Although solar electromagnetic radiation is by far the dominant source of energy to the Earth, the actual contribution of solar forcing to recent climate change is hotly debated. Therefore, over the past decades, scientists have been investigating the unique relationship between the Sun and the Earth. Using space-based tools, like the extreme ultraviolet imaging telescope on the solar and heliospheric observatory (SOHO), they have calculated the amount of solar energy that reaches the outer atmosphere, the so-called solar irradiance. The SOLID (First European comprehensive solar irradiance data exploitation) project with the support of EU funds aimed to merge all observations scattered in disperse data sets. One single homogeneous solar irradiance record is vital to untangling the role that changes in solar radiation have on global climate. Representatives of all European space-based solar experiments, European researchers specialising in solar image processing and solar irradiance modelling joined SOLID in their efforts. Project partners used state-of-the-art methodologies to fill gaps in time and wavelengths as well as to reduce noise and associated uncertainties. A pre-processing scheme addressed issues related to data gaps and outliers and aimed to reduce noise. Researchers focused on identifying a procedure for reconstructing daily time series of solar irradiance variations using magnetograms simulated with a surface flux transport model. The project developed a total and spectral irradiance (SSI) database based on multi-wavelength solar radio observations covering the last century. The simulated magnetograms provided the spatial distribution of active regions on the surface of the Sun. The reconstructed time series are publicly available on the website of the Max Planck institute for Solar system research. The making of the SSI dataset, however, is not yet complete. This is a continuing process, as new data are being produced, physical models are improving and the needs of the user community become more specific. The experience gained by project partners is invaluable for defining more durable SSI products, which can be used by the wider user community and help shape a European strategy. SOLID has made a tremendous contribution to the scientific community by combining all existing observations of solar irradiance and the final record should cover the entire spectrum of solar wavelengths. Moreover, its enhanced accuracy will help to accurately determine the Sun's direct and indirect effects on Earth's climate change.
Keywords
Solar irradiance, heliospheric observatory, SOLID, magnetograms, spectral irradiance