1. Atmospheric Radio Soundings in Argentina - Effects of Air Density Variations - Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Bianca KeilhauerTokyo, February 26th, 2004

2. 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

3. Important Effects of Atmospheric Profiles X to h transmission 1.Atmospheric depth to geom. height 2.Fluorescence light production fl. yield λ (p,T) 3.Fluorescence light transmission τ (p,T) Fl. Yield telescope on the Auger FD shower data height atmosph. depth Fe p p fluorescence photons

4. Geometrical Effect particle number (x 10 9 ) atmospheric depth (g/cm²) height (km a.s.l.) 10 8 6 5 4 3 2 10 19 eV / 0° US Std. atmosphere Fe p atmospheric depth: air density: ⇒ height and time dependent

5. Atmospheric Depth Profiles Max. of Fe-ind. 10 19 eV, 60 o shower in US-StdA  distortion of longitudinal shower profiles  shift of position of shower maximum averaged measured profiles:

6. Difference in Atmospheric Depth within seasons summer, January / February 2003 winter, July / August 2003

7. Longitudinal Shower Development - Energy Deposit - ⇒ Δh max = 436 m between winter I and summer atmosphere average of 100 simulated showers ⇒ same EAS in N e (X) for all atmospheres

8. Difference in Energy Deposit same EAS in N e (X) for all atmospheres

9. Fluorescence Yield for a 1.4 MeV electron, vertical incidence EAS excites N 2 – molecules in air de-excitation partly via fluorescence light emission (λ ≈ 300 -400 nm) fl. yield ~ local energy deposit

10. Position of Shower Maximum - Fluorescence Yield - both EAS in US-StdA, 60°, 10 19 eV: → Δh max = 800 m vertical height difference 7.6 km 8.4 km both EAS 60°, 10 19 eV, p-ind. in summer, Fe-ind. in winter I: → Δh max = 350 m vertical height difference 8.0 km 8.35 km both 8.1 km same EAS in N e (X) for all atmospheres

11. X max distribution for Fe-ind. showers with 60° N_entry Mean in g/cm²RMS 100069220.9 500071326.1 ⇒ increase of X max distribution by approx. 25 % same EAS in N e (X) for all atmospheres

12. Photons at the telescope Fe, 10 19 eV, 60°, same EAS in N e (X) for all atmospheres

13. Photons at the telescope Fe, 10 19 eV, 60°, same EAS in N e (X) for all atmospheres

14. Summary Atmospheric conditions influence the: - Shower development - Fluorescence light emission - Light transmission EAS profiles are shifted and distorted: - X max position - Energy reconstruction - Distribution of X max broadened in dependence of incidence angle (more important for Fe-ind. EAS than for p-ind. ) Fluorescence yield is height and (p,T) - dependent

15. 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

16. Atmospheric Depth Distribution at 2400 m for the individual profiles measured in Argentina N_entry Mean in g/cm²RMS 617834 157852 117835,5 177814,7 187832,2

17. Atmospheric Depth Distribution at 8400 m for the individual profiles measured in Argentina N_entry Mean in g/cm²RMS 613578,2 153651,7 113594,6 173487,6 183585,3