Forschungszentrum Karlsruhe
in der Helmholtz-Gemeinschaft
Atmospheric Radio Soundings in Argentina
- Effects of Air Density Variations -
Bianca Keilhauer
Tokyo, February 26th, 2004
Data Acquisition
• Auger Fluorescence Detector measures longitudinal shower development
• Atmospheric parameter affect the development and detection at every height
⇒ Knowledge of atmospheric profiles is required
Radiosonde measurements in each season are performed:
 61 successful launches in total
 Average reached altitude ≈ 20 km a.s.l. (maximum was 28 km a.s.l.)
 Roughly every 20 m a set of data (h, p, T, u, wind)
 Used DFM-97 GPS sondes (www.graw.de)
 Accuracy: T < 0.2 K
p < 1.0 hPa (range 200 hPa to 1080 hPa)
< 0.5 hPa (range 5 hPa to 200 hPa)
u < 5%
Important Effects of Atmospheric Profiles
on the Auger FD shower data
1. Atmospheric depth to geom. height

X    z  dz
dE
dx
fluorescence photons
h
X to h
2. Fluorescence light production
fl. yieldλ (p,T)
3. Fluorescence light transmission
p
τ (p,T)
telescope
Fe
Fl. Yield
height
h km 
p
Fe
atmosph. depth

X  g

 cm ² 
atmospheric depth (g/cm²)
height
(km a.s.l.)
particle number (x 109)
10
8
Geometrical Effect
atmospheric depth:

Fe
p
X     z  dz
h
6
5
air density:
4
 ( z) 
p( z )  M m
R  T ( z)
1019eV / 0°
3
US Std. atmosphere
2
⇒ height and time dependent
Atmospheric Depth Profiles
Max. of Fe-ind. 1019eV, 60o
shower in US-StdA
averaged measured
profiles:
 distortion of
longitudinal
shower profiles
 shift of position
of shower
maximum
Difference in
Atmospheric Depth
within seasons
winter,
July / August 2003
summer,
January / February 2003
Longitudinal Shower Development
- Energy Deposit -
average of 100 simulated
showers
⇒ same EAS in Ne(X)
for all atmospheres
⇒ Δhmax = 436 m
between winter I and
summer atmosphere
Difference in Energy Deposit
same EAS in Ne(X) for all atmospheres
Fluorescence Yield
for a 1.4 MeV electron, vertical incidence
• EAS excites N2 –
molecules in air
• de-excitation
partly via
fluorescence light
emission
(λ ≈ 300 -400 nm)
• fl. yield ~ local
energy deposit
Position of Shower Maximum
- Fluorescence Yield 7.6 km
8.4 km
both EAS in US-StdA, 60°, 1019eV:
→ Δhmax= 800 m vertical height difference
8.0
km
8.35
km
both
8.1 km
same EAS in Ne(X)
for all atmospheres
both EAS 60°, 1019eV,
p-ind. in summer,
Fe-ind. in winter I:
→ Δhmax= 350 m vertical
height difference
Xmax distribution for
Fe-ind. showers with 60°
N_entry
Mean in
g/cm²
RMS
1000
692
20.9
5000
713
26.1
⇒ increase of Xmax
distribution by approx.
25 %
same EAS in Ne(X)
for all atmospheres
Photons at the telescope
Fe, 1019eV, 60°, same EAS in Ne(X) for all atmospheres
Photons at the telescope
Fe, 1019eV, 60°, same EAS in Ne(X) for all atmospheres
Summary
• Atmospheric conditions influence the: - Shower development
- Fluorescence light emission
- Light transmission
• EAS profiles are shifted and distorted: - Xmax position
- Energy reconstruction
- Distribution of Xmax broadened in
dependence of incidence angle
(more important for Fe-ind. EAS
than for p-ind. )
• Fluorescence yield is height and (p,T) - dependent
Difference of Atmospheric Depth Profiles
for pressure at ground: 825.0 ± 0.2 hPa,
829.0 ± 0.2 hPa,
826.0 ± 0.2 hPa,
834.5 ± 0.2 hPa
Atmospheric Depth Distribution at 2400 m for
the individual profiles measured in Argentina
N_entry
Mean in
g/cm²
RMS
61
783
4
15
785
2
11
783
5,5
17
781
4,7
18
783
2,2
Atmospheric Depth Distribution at 8400 m for
the individual profiles measured in Argentina
N_entry
Mean in
g/cm²
RMS
61
357
8,2
15
365
1,7
11
359
4,6
17
348
7,6
18
358
5,3