Simulations of detector arrays and the impact of atmospheric parameters

In Monte-Carlo simulations of gamma-ray or cosmic-ray detector arrays on the ground (here mainly arrays of imaging atmospheric Cherenkov telescopes), the atmosphere enters in several ways: in the development of the particle showers, in the emission of light by shower particles, and in the propagation of Cherenkov light (or fluorescence light or of particles) down to ground level. Relevant parameters and their typical impact on energy scale and so on are discussed here.