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

太阳对气候的影响是关于全球变暖和过去气候变化原因的辩论中的主要未知数之一。尽管太阳对气候的影响的证据越来越多，但太阳可变性的起源以及可变的太阳输入影响气候变化的过程还不是很清楚。地球气候的主要太阳量是太阳总辐照度和光谱辐照度。太阳辐照度的测量揭示了从几分钟到几十年的所有采样时间尺度的变化。不幸的是，测量到的辐照度时间序列太短，无法计算出与地球气候变化的准确联系，必须在适当模型的帮助下将时间延长。模型的一个重要任务是确定观测到的辐照度变化的原因。我们打算在以前工作的基础上，通过对太阳磁化大气的动态三维结构的数值模拟，严格检验太阳辐照度变化是由表面磁场的演变引起的这一假设。模型的另一个主要目标是重建比直接观测采样时间更长的时间尺度上的辐照度。在这里，主要的争议围绕着太阳辐照度可能发生的长期变化的幅度。我们建议使用太阳的历史照片来确定它在20世纪变亮了多少。最后，模型面临的主要挑战之一是预测未来的辐照度变化。我们建议使用一个有希望的参数，太阳黑子群的倾角来预测太阳活动的水平，并由此预测未来的辐照度。

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.