Abstract:
The air fluorescence detector of the Pierre Auger Observatory is designed to perform calorimetric measurements
of extensive air showers created by cosmic rays of above 1018 eV. To correct these measurements
for the effects introduced by atmospheric fluctuations, the Observatory contains a group of
monitoring instruments to record atmospheric conditions across the detector site, an area exceeding
3000 km2. The atmospheric data are used extensively in the reconstruction of air showers, and are particularly
important for the correct determination of shower energies and the depths of shower maxima.
This paper contains a summary of the molecular and aerosol conditions measured at the Pierre Auger
Observatory since the start of regular operations in 2004, and includes a discussion of the impact of these
measurements on air shower reconstructions. Between 1018 and 1020 eV, the systematic uncertainties
due to all atmospheric effects increase from 4% to 8% in measurements of shower energy, and 4 g cm 2
to 8 g cm 2 in measurements of the shower maximum.
