Description of atmospheric conditions at the Pierre Auger Observatory using the Global Data Assimilation System (GDAS) - Abreu, P.; Albuquerque, Ivone Freire da Mota e; Souza, Vitor de; Gouffon, Philippe; Peixoto, C. J. Todero; Tridapalli, D B (Astroparticle Physics, 2012)