Total spectral irradiance is typically modelled by assigning an atmospheric model to each pixel of a full disk image and geometricllay combining the predicted wavelength dependent intensity for each of these models into a disk integrated spectrum. This works reasonably well, as the hydrostatic models that are used in this procedure generally reproduce observed spectra very well. However, for numerical expedience this scheme neglects some important physical aspects of the the solar atmosphere, in particular its three-dimensional structure and strongly dynamic nature.
In this talk I will discuss the importance of some of these effects on the spectral irradiance signal, using forward radiative transfer modeling in realistic three-dimensional and time dependent simulations. Characterizing the contributions from spatial inhomogeneity and temporal variation will also help us to better understand the physical
nature of the forces that drive variability, and hopefully improve our predictive capabilities.