Modelling solar irradiance variations: the influence of faculae and small-scale magnetic flux elements

太阳是地球气候的主要驱动力。然而，它的可变性对气候的影响仍然知之甚少。这是由于多种原因造成的，其中包括缺乏对这种影响普遍接受的机制，难以明确地将复杂气候系统中的信号归因于太阳，以及在与气候有关的时间尺度上太阳总变率和光谱变率水平存在很大不确定性。这项提议旨在提供最先进的太阳辐射重建，覆盖从UV到IR的所有波长。这将在两个主要方面比目前的重建有很大的改进：1)我们建议将部分UV光谱的非LTE光谱合成计算与可见光和IR的标准LTE计算结合起来。LTE计算在大多数可见光和红外区域都足够准确，并且计算简单。我们将在最需要它们的地方用非LTE计算来补充这些计算，即我们目前的LTE计算已知失败的地方。紫外线波长区的可变性特别令人感兴趣，因为它是目前最有希望提供太阳-气候耦合的机制。2)我们将从磁对流模拟中得到亮磁元的强度。这将使我们第一次获得小规模磁性元素的光谱响应，这些元素被认为是长期辐照度变化的主要原因。据我们所知，这是目前估计长期光谱变率的唯一方法。此外，磁对流模拟可以用来得到合成磁图，然后可以用来将观测到的磁图信号转换成强度，从而省去了辐射重建中的任何自由参数。作为副产品，我们将通过获取太阳表面图像来测试模拟，这些图像可以直接与观测结果进行比较，例如Hinode或Sun里斯拍摄的图像。

The Sun is the main driver of the Earth's climate. The effect of its variability on the climate, however, remains poorly understood. This is due to a number of reasons, including the lack of a universally accepted mechanism for such an influence, the difficulties in attributing signals in the complex climate system unambiguously to the Sun as well as large uncertainties regarding the level of total and spectral solar variability over climate-relevant time scales. This proposal aims to provide state-of-the art solar irradiance reconstructions spanning all wavelengths from the UV to the IR. These will represent a major improvement compared to current reconstructions in two main respects: 1) We propose to combine non-LTE spectral synthesis calculations in parts of the UV spectrum with standard LTE calculations in the visible and IR. LTE calculations are sufficiently accurate over most of the visible and IR region and are computationally straightforward. We will complement these with non-LTE calculations where they are most needed, i.e., where our current LTE calculations are known to fail. The variability in the UV wavelength region is of particular interest as it currently the most promising mechanism to provide the Sun-climate coupling. 2) We will derive the intensities of the bright magnetic elements from magneto-convection simulations. This will allow us for the first time to obtain the spectral response for the small-scale magnetic elements that are thought to be the main cause for long-term irradiance variability. To our knowledge, this is currently the only way to estimate the long-term spectral variability. In addition, the magneto-convection simulations can be used to derive synthetic magnetograms that can then used to translate the observed magnetogram signals into intensities, thus dispensing with any free parameters in the irradiance reconstructions. As a by-product, we will test the simulations by deriving solar surface images that can be directly compared to observations, such as those taken by, e.g., Hinode or Sunrise.