Atmospheric Radio Soundings in Argentina

- Effects of Air Density Variations -

Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft

Bianca Keilhauer Tokyo, February 26th, 2004

• 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%

Data Acquisition

Important Effects of Atmospheric Profiles

dx

dE

²cmgX kmh

X to h

transmission

1. Atmospheric depth to geom. height

2. Fluorescence light production

fl. yieldλ (p,T)

3. Fluorescence light transmission

τ (p,T)

h

dzzX

Fl. Yield

telescope

on the Auger FD shower data

height atmosph. depth

Fep

Fep

fluorescence photons

Geometrical Effect

particle number (x 109)

atm

osph

eric

dep

th (

g/cm

²)height (km a.s.l.)

10

8

6

5

4

3

2

1019eV / 0°

US Std. atmosphere

Fe

p

h

dzzX

atmospheric depth:

air density:

)(

)()(

zTR

Mzpz m

⇒ height and time dependent

Atmospheric Depth ProfilesAtmospheric Depth Profiles

Max. of Fe-ind. 1019eV, 60o shower in US-StdA

distortion of longitudinal shower profiles

shift of position of shower maximum

averaged measured profiles:

Difference in Atmospheric Depth

within seasons

summer,

January / February 2003

winter,

July / August 2003

Longitudinal Shower Development

- Energy Deposit -

⇒ Δhmax = 436 m between winter I and summer atmosphere

average of 100 simulated showers

⇒ same EAS in Ne(X) for all atmospheres

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 -

both EAS in US-StdA, 60°, 1019eV:

→ Δhmax= 800 m vertical height difference

7.6 km 8.4 km

both EAS 60°, 1019eV, p-ind. in summer, Fe-ind. in winter I:

→ Δhmax= 350 m vertical height difference

8.0 km

8.35 km

both 8.1 km

same EAS in Ne(X) for all atmospheres

Xmax distribution for Fe-ind. showers with

60°

N_entryMean 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_entryMean 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_entryMean in g/cm² RMS

61 357 8,2

15 365 1,7

11 359 4,6

17 348 7,6

18 358 5,3