For the reconstruction and simulation of extensive air showers, it is necessary to know the atmospheric
conditions at the place of the experiment. Therefore, several systems for atmospheric monitoring have
been installed at the Auger South array.
The atmosphere will be described by the following state variables in dependence of altitude:
- temperature [K]
- pressure [hPa]
- density [kg/m³]
- atmospheric depth [g/cm²]
- relative humidity [%]
- wind speed [m/s]
- wind direction [°]
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Measurement Techniques
For measuring the variables describing the molecular part of the atmosphere in dependence of altitude, the
Karlsruher Auger group performs meteorological radio soundings.
The atmospheric profiles are obtained typically
from Auger-level (about 1450 m a.s.l.) up to 25 km a.s.l. Additionally,
ground-based weather stations record
the same set of variables in 5 min. intervals. Between March 2009 and end 2010, we participated with the socalled
Balloon-the-Shower programme in the Radid Atmospheric Monitoring Programme of the Pierre Auger
Observatory. All incoming air shower events, which are detected by the fluorscence telescopes, are reconstructed
immidiately. An analysis of these data within 10 min. after the air shower event selects the highest-energy and
well-observed events and triggers a dedicated launch of a weather balloon.
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Database and ASCII Tables
The data are stored in a database for the molecular atmoshere, and are available for members of the
Auger collaboration for reconstructions and simulations.
It is a MySQL database.
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Atmosphere - Data and Models
The atmospheric conditions in dependence on altitude show large temporal fluctuations. Therefore, in addition to
actual measurements, also models may be useful. Within the Auger collaboration, models
with different validities for time and space have been developed. Early 2009, very precise monthly models for
the area of the Pierre Auger Observatory at the Pampa Amarilla, Argentina, were derived. Based on the experiences
with the Balloon-the-Shower programme, we could substitute local radio soundings by data from the
GDAS - Global Data Assimilation System.
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Effects on Cosmic Rays
The atmsophere influences the development and the detection of Ultra High Energy Cosmic Rays (UHECR)
at several stages. The physical consequences of the atmospheric variability are discussed in various
publications.
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The measurement of extensive air showers can be performed by using the
fluorescence technique. Electrons and positrons of extensive air showers
excite nitrogen molecules in the Earth's atmosphere and the de-excitation
happens via emission of fluorescence light, mainly in the wavelength region
between about 280 and 420 nm.
Atmospheric dependences have to be implemented in the air shower
reconstruction for a proper description of the fluorescence emission.
Temperature, pressure, and humidity effects, especially at the
de-excitation processes of the nitrogen molecules, are subject of
current research.
The progress in this research field is discussed
at regular workshops since several years:
FIWAF 02 -
Utah, USA, 2002
Air Light 03 - Bad
Liebenzell, Germany, 2003
IWFM 05 -
Habere-Poche, France, 2005
4th air
fluorescence workshop - Prague-Pruhonice, Czech Republik, 2006
5th Fluorescence
Workshop - El Escorial-Madrid, Spain, 2007
6th Air Fluorescence Workshop
- L'Aquila, Italy, 2009
7th Air Fluorescence Workshop
- Coimbra, Portugal, 2010
8th Air Fluorescence Workshop
- Karlsruhe, Germany, Sept. 2011
Currently, an international working group is developing a description
of the nitrogen fluorescence in air, which might be used by all experiments
for cosmic rays. The working group was established at the 8th Air
Fluorescence Workshop and presented first results at the
International Symposium on Future Directions in UHECR Physics 2012.