title: Problem of incident radiation in 2D non-LTE modeling of solar prominences authors: Julius Koza, Pavol Schwartz, Stanislav Gunar, Petr Heinzel abstract: The Lyman-alpha and Mg II h & k resonance lines are among the most prominent spectral lines observed in the solar UV spectrum on the disk. As such, they represent a significant source of illumination of prominences affecting ionization of prominence plasma and also provide a fundamental diagnostics tool for these low-density structures. The talk reports about status of our project aimed at advanced spectral diagnostics of quiescent solar prominence observed in 2013 quasi-simultaneously in the lines of Lyman series and Mg II h & k by the SUMER spectrometer aboard the SoHO spacecraft and the Interface Region Imaging Spectrograph (IRIS). The analysis itself will be accomplished by already-existing 2D model of solar prominence implemented in pertinent codes solving self-consistently the problem of non-LTE radiative transfer in the hydrogen lines and the lines of ionized magnesium. The modeling requires definition of accurate incident radiation, illuminating a prominence from the solar disk, as a key boundary condition in calculations. To this purpose we create new reference disk-averaged profiles of the Lyman-alpha and Mg II h & k lines and create models of their variation over the solar cycle. We use a set of dedicated Lyman-alpha raster scans obtained over extended periods by the SUMER/SoHO spectrometer and series of full-disk IRIS mosaics in Mg II h & k. This approach advances prominence modeling toward higher level of physical realism. The analysis of the influence of the cyclic change in the Lyman-alpha incident radiation shows that the synthetic prominence spectra are strongly affected by the modification of the incident radiation boundary condition. The hydrogen H-alpha line can also be considerably affected, despite the fact that the H-alpha radiation from the solar disk does not vary with the solar cycle. While the disk Lyman-alpha profile does not show center-to-limb variation the Mg II h & k do so showing a limb darkening. We also create a new analytic model of cyclic variation of disk-averaged Mg II h & k profiles parametrized by the Bremen composite Mg II index. We find that the model is accurate in more than 90% of profile reconstructions. This talk is complementary to the talk by Pavol Schwartz.