Models of solar total and spectral irradiance variability of relevance for climate studies

点击翻译按钮获取中文摘要

The influence of the Sun on climate is one of the major unknowns in the debate on global warming and on the causes of past climate changes. Although the evidence for solar influence on climate is growing, the origin of solar variability and the processes by which the variable solar input affects climate change are not well understood. A prime solar quantity for the Earth’s climate is solar total and spectral irradiance. Measurements of solar irradiance have revealed variations at all the sampled time scales from minutes to decades. Unfortunately, the measured irradiance time series is too short to work out the precise connection with climate change on Earth and has to be extended back in time with the help of suitable models. One important task of models is to identify the causes of the observed irradiance variations. We propose to build upon our previous work and rigorously test the hypothesis that solar irradiance variations are caused by the evolution of the surface magnetic field through the use of numerical simulations of the dynamic 3-D structure of the Sun’s magnetised atmosphere. Another major aim of the models is to reconstruct irradiance over time scales longer than sampled by direct observations. Here the main controversy surrounds the magnitude of the possible secular change of solar irradiance. We propose to use historic photographs of the Sun to determine by how much it has brightened in the 20th century. Finally, one of the main challenges to models is to predict future irradiance variations. We propose to employ a promising parameter, the tilt angles of sunspot groups to predict the level of solar activity and from that irradiance in the future.