Atmospheric observations either from space and ground are obtained at different local times. Because of the diurnal solar forcing and the photochemistry, dynamical parameters and chemical species exhibit systematic fluctuations over a period of 24 hours or related harmonics. Such fluctuations are often larger than expected agreements during instrumental inter-comparisons and inter-annual change investigations either natural or anthropic. When the solar-time of the measurements varies or are different, it could be a source of uncertainty. While most of these fluctuations are known to exist, their exact amplitude as a function of altitude and season, and their variability under different forcing are not well known. Also there is a strong need for long-term satellite validations while the orbits of the space platforms drift. The validation of these fluctuations simulated in numerical climate models can be also of interest to validate radiative schemes and could be important for improving assimilation attempts of data satellite in numerical models. Methods developed to overcome these limitations or satellite validation/data comparisons showing such problems could be discussed during this session.