Auger at the University of Wisconsin, Madison

Atmospheric Monitoring

Our atmosphere monitoring section is only available to members of the Auger collaboration.

Description of Activities

The Pierre Auger Observatory, located outside of Malargüe, Argentina, is the world's largest detector of ultra-high-energy cosmic rays. These particles are of unknown origin, and are detected at Earth via the extensive air showers of particulate and ultraviolet radiation they create in the atmosphere.

Central Laser Facility
Central Laser Facility

Comprising the Auger detector is a massive array of ground stations used to sample air shower particles at Earth's surface, as well as four fluorescence detectors which observe the UV light generated during shower development. The surface array, running day and night in all weather conditions, records significant numbers of events and provides the primary statistics of the experiment. The fluorescence detectors, running during moonless nights only, make a calorimetric measurement of cosmic ray energies, and so are used to calibrate the energies of particles observed in the ground array.

Because the fluorescence detectors operate in widely varying atmospheric conditions, Auger has instituted a broad program of nightly atmospheric monitoring. The thrust of the program is to characterize the absorption and scattering of ultraviolet light as it propagates from an air shower to the fluorescence detectors. The aim of monitoring is to correct fluorescence observations for changing atmospheric conditions, and thereby contribute to the absolute calibration of the observatory's energy measurements.

Lidar station at Los Leones
Lidar Leones

The backbone of the atmospheric montoring system is provided by UV laser scattering observations of the atmosphere. These observations are carried out by two types of detectors: a Central Laser Facility (CLF) positioned in the center of the ground array; and backscatter Lidar stations located next to each fluorescence detector. The two detector types yield redundant measurements of light scattering by aerosol layers. Moreover, the CLF can be used to determine the pointing of each fluorescence detector, while the Lidar stations have the capability to "shoot the shower" — i.e., aim a series of laser shots along the track of a detected shower, and so directly observe the atmospheric scattering properties between the shower track and the fluorescence detectors.

Additional measurements of the aerosol properties of the atmosphere are being carried out by an Aerosol Phase Function Monitor (APF) located at each fluorescence site and a Horizontal Attenuation Monitor (HAM). Observations of the molecular component of atmospheric scattering occur during regular balloon-based meteorological radio soundings. And finally, photometric calibrations of the atmosphere using bright stars are being performed by the (F/Ph)otometric Robotic Atmospheric Monitor (FRAM) located at Los Leones.