The SIRTA team takes care of the national multi-instrumental observatory dedicated to the observation of the atmosphere, located at the Ecole Polytechnique. The SIRTA was founded in 1999 on the initiative of the IPSL to federate the research (fundamental or applied) and teaching activities of laboratories in the Paris region in the fields of atmospheric instrumentation and measurements. The SIRTA is a reference tool at the European and international levels. With regard to the contribution of the LMD to the SIRTA operation in terms of technical support and scientific research, a team dedicated to the LMD is studying more particularly the impacts of clouds on the regional climate, the processes driving winter low clouds and fog and summer convective clouds that can create violent thunderstorms, the nature of the different sources of aerosols encountered in the Paris region and the impact of aerosols and clouds on the variability and predictability of photovoltaic electricity production in real conditions.