Atmospheric monitoring and its impact on air shower observables at the Pierre Auger Observatory

The Pierre Auger Observatory, completed in September 2008, detects cosmic rays by observing and studying the development of extensive air showers in atmosphere. The atmosphere itself, with its unpredictable changes of conditions, directly influences the estimation of the air shower characteristics. In this paper, all the instruments and techniques adopted by the Auger Observatory are explained, and the impact of their results on the most important shower parameters are shown.