  The dependence of atmospheric conditions on altitude and time have to be
known at the site of an air shower experiment for accurate reconstruction of
extensive air showers and their simulations. The height-profile of atmospheric
depth is of particular interest as it enters directly into the reconstruction
of longitudinal shower development and of the primary energy and mass of cosmic
rays. For the southern part of the Auger Observatory, the atmosphere has been
investigated in a number of campaigns with meteorological radio soundings and
with continuous measurements of ground-based weather stations. Focussing on
atmospheric depth and temperature profiles, temporal variations are described
and monthly profiles are developed. Uncertainties of the monthly atmospheres
that are currently applied in the Auger reconstruction are discussed.
