Almost four decades of space-based solar irradiance monitoring have enriched us with a great amount of data from numerous experiments at different wavelengths. The utility of the available total and spectral irradiance records for atmospheric and climate research is, however, limited by their inhomogeneous and incomplete wavelength and temporal coverage and often by limited instrument stability. Currently only irradiance models can fill these gaps and furnish us with records that are more homogeneous and complete in wavelength coverage than the observations. Two kinds of models, proxy and semiempirical, have been developed. Their products differ from each other in ways that are critical for modelling climate change. There is thus a strong need to understand the causes of differences between model outputs and to identify ways of overcoming model shortcomings. This team includes experts representing both kinds of models.

The quality and reliability of the output of irradiance models is of crucial importance for the broad Earth- and solar-research communities, as can be judged from the various national and international projects addressing related issues. Thus the EU FP7 SOLID, NASA SIST, ISSI SHAPE, ISSI “An Assessment of the Accuracies and Uncertainties in the Total Solar Irradiance Climate Data Record,” and SNSF SILA projects evaluated the quality of different measured total and spectral irradiance data sets and made efforts to crosscalibrate some of the records. The German ROMIC/MUSIC project has taken steps towards significantly more physically consistent models. Related topics are also addressed by the ongoing ISSI team “Towards New Models of Solar Spectral Irradiance based on 3D MHD Simulations” (ID335). The progress in these individual areas provide a solid foundation for tackling the most pertinent issue – the lack of a sufficiently long, homogeneous and reliable solar irradiance record as required by global circulation and climate models.

The main goal of this team, which includes experts in solar irradiance instrumentation, observations, data analysis and modelling, as well as atmospheric and climate scientists, is to fill this gap and reach a consensus on a single and homogeneous modelled irradiance record to recommend to the climate community. This effort will also include realistic estimates of the remaining uncertainties. This team will play a central role in forming such a consensus, which will be summarized in a review article and later presented to and discussed within the wider community in a separate and larger meeting (to be organized outside ISSI).

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