J. Alvarez-Castillo 1 and J. F. Valdés-Galicia 1 , for the Pierre Auger Collaboration 2

1. 1 Space Sciences, Geophysical Institute, UNAM, Mexico City, Mexico. 2 Pierre Auger Observatory, Malargüe, Mendoza, Argentina. Atmospheric Effects in the Electromagnetic Component of the Secondary Cosmic Rays in the Pierre Auger Observatory J. Alvarez-Castillo1 and J. F. Valdés-Galicia1, for the Pierre Auger Collaboration2 IS@O, April 2011

2. History The increase of the counting rate was only about 1%. Alexeenko et al. 1985, 2002 1985:−1% hard + 2% soft 2002: Different effects for hard and soft components. Aglietta et al., 1999 Increase of 5% of the counting rate. Muraki et al., 2004 The increase of the counting rate was only about 1%. González & Valdés-Galicia, 2006 Alvarez-Castillo & Valdés-Galicia, 2010 Variations of ±0.5-1% of the counting rates on average for hard and soft components. Alvarez-Castillo & Valdés-Galicia, this work

3. The Pierre Auger Observatory The Pierre Auger Observatory is located in the Southern Hemisphere, in the area of Malargüe city, Mendoza Province, Argentina. The Auger Observatory consists of an array of 1,600 water Cherenkov detectors, on a 1.5 km in an hexagonal grid covering 3,000 km2. The surface detector network is complemented by fluorescence detectors and weather stations.

4. Thunderstorm Quiet Day Red= Electric Field (EF); Blue= CR (Cosmic Rays) EF during Thunderstorms(TS) >1,000 V/m, EF in Quiet Days (QD) < 200 V/m. Fluctuations are different: In QD the most important variation is the diurnal variation. In TS both disturbances are coupled.

5. Data Selection • CR close to the solar minimum (2007/11/27-2010/01/22). • Data with large variations in the geomagnetic field (kp > 20) and Forbush decreases were discarded. • Correction for pressure was made, other effects were not considered, as they are of minor importance. • TS were defined as measurements of |EF| > 800 V/m. • QD were selected considering measurements of |EF| < 200 V/m. • WD are considered with measurements of 200 < |EF| < 800 V/m. • Other atmospheric variables were considered (temperature, pressure and humidity). • Data resolution for this study is five minutes.

6. Methodology All data during electric storms, quiet and windy days were filtered, removing the lowest frequencies. An analysis of frequency-time (wavelet) was performed to the data, obtaining the periodicities of these. Signals were compared in time and frequency. One second SD scaler data were processed to eliminate anomalies due to jumps in the PMT baselines(Not considered in this presentation).

7. Filtered CR data (five minute resolution) The Filtering of the CR data during a day with a thunderstorm (2007/12/25), is shown in the bottom panel, the two sigma level is exceeded from 13:45 to 19:10 UTC, when a TS occurred. Trend Filtered Original data Interval of the effects of the Thunderstorm 2 σ

8. Wavelet Spectrum Interval of the TS effects on the EM component Time serie of normalized data highest power Spectrogram red noise lowest power • Note: • Red noise is calculated dynamically considering each time series. • Sigma normalization data.

9. Wavelet analysis during thunderstorms (five minute resolution 25/12/2007) Peaks in the Spectrum are at 5 hr, 2 hr and also around 30 min. Beyond 15 min. the signal is confused with the red noise level. EF spectrum shows two peaks: one with a maximum around 30-45 min., another around 6 hours, below the red noise. FLUCTUATIONS ARE MUCH STRONGER DURING TS

10. Temperature Humidity Pressure Electric Field Cosmic Rays Wind Speed

11. Wavelet analysis in quiet days(five minute resolution 20/03/2008) Two peaks are present: around 30 min and one hour. Other two peaks are close to the red noise level: 3.15 hours and 6 hours. Periodicities in EF are: one around 20 minutes, another from 4 to 6 hours (maximum at 5 hours), and a small peak close to 3 hours. FLUCTUATIONS ARE SPARSE, HF IS UNCORRELATED

12. Temperature Humidity Pressure Electric Field Cosmic Rays Wind Speed

13. Filtered data (2007/12/08) Pressure Temperature Relative Humidity Wind Speed Electric Field Cosmic Rays

14. Temperature Humidity Pressure Electric Field Cosmic Rays Wind Speed

15. CR and EF summary We worked with 12 TS and 21 QD Thunderstorms days: WE SEE HARMONIC VARIATIONS IN CR AND EF (TUNED) Periodicities present: Quiet days: HF VARIATIONS ARE UNCORRELATED. Periodicities present:

16. Possible explanations for periodicities • The periodicities of 30min, in CR and EF could be related to electric field transitions, known to exist higher in the atmosphere (Israel, 1971) • The periodicities of half hour and less in EF and CR, with some intermittency, may be connected with microburst wind, that potentially carries large amounts of dust, whose composition in Malargüe is mostly iron (FIP 8 eV), that could be electrically charged (Rasmussen et al., 2009). • The 2 hour periodicity in CR and EF could be related to light and gentle wind, carrying charged particles and ions (Reiter, 1992). The CR variation of around 6 hours is due to the fourth harmonic diurnal variation of the EF.(Bhartendu, 1972). • Other low frequency variationsin CR during TS may be due to rain. Rain droplets carry unstable particles that decay and contribute to changes in the flow of the CR; for this reason these variations are not present in the EF [Aglietta et al., 1999; Vernetto , 2001; Alexeenko et al., 2007].

17. SUMMARY The main contributions of this work are: • During thunderstorms electric field and cosmic rays variations are coupled. 2. The variations in the electric field are composed of two frequencies: a high frequency of a few minutes and a low frequency of a few hours. The high frequency is intermittent and is due to the existence of high intensity EF (higher than ±4,000 V/m) during thunderstorms. The low frequency may be connected to the wind flow that carries particles and ions that build the EF, it is present in QD. The atmospheric electric field is, to a significant extent, due to charged particles and ions in the air, that generally tend to have a net positive charge (Reiter, 1992). 3. The intermittent EF and CR fluctuations that are coincident may be connected with microburst wind, that potentially carries large amounts of dust and ions. (Rasmussen et al., 2009)

18. Acknowledgments • The successful installation and commissioning of the Pierre Auger Observatory would not have been possible without the strong commitment and effort from the technical and administrative staff in Malargüe. • M. in P. Hernán Asorey and Dr. Xavier Bertou for technical support in the Auger observatory data in the Centro Atómico Bariloche (San Carlos de Bariloche, Río Negro, Argentina). • CONACYT (Consejo Nacional de Ciencia y Tecnología) for the scholarship awarded me for the completion of doctoral. • We are very grateful to the following agencies and organizations for financial support in the Pierre Auger Observatory:

19. Thank you very much for your kind attention!

20. Tank selection for one second data resolution

21. Wavelet analysis during thunderstorm(one second resolution)

22. SCR Global spectrum at high frequencies Periodicities of 0-90 seconds Periodicities of 0-20 seconds

23. Periodicities summary (secs)

24. Electric field spectrum The periodicities ranging from 4 to 64 seconds!!

25. Preliminary Results(one second resolution) • Temporal resolution data of a second are useful to see the effects of lightning on the electromagnetic component of cosmic rays. Very large increases covering a range from 5-25 standard deviations, depending of the intensity of the discharge. • Much of the variation present in cosmic rays are caused by an electric effect, which can be: redistributions of charges, electric shock or resonant effects, in the range of 4-64 seconds. • Periodicities<4 sec in SCR, are possibly due to the Runaway BreakdownProcess. The presence of a strong electric field in a thundercloud causes the acceleration of energetic electrons, which through collisions generate more fast electrons, which in turn will be also accelerated, causing a cascading effect that leads to a large flow of electrons producing the electric discharge (Gurevich et al, 1999).

26. Departamento de Ciencias Espaciales 1 A partir de un campo eléctrico de alta tensión, nace la formación de la descarga

27. Departamento de Ciencias Espaciales 2 La constante de Ionizacion del aire

28. Departamento de Ciencias Espaciales 3 Genera una concentración de cargas puntual, donde aparecen los trazadores

29. Departamento de Ciencias Espaciales 4 y abren el camino ionizado de conexión, y la descarga eléctrica aparece

30. Departamento de Ciencias Espaciales 5 El aire queda saturado eléctricamente

31. Departamento de Ciencias Espaciales 6 Y el proceso se puede repetir mas rápidamente

32. Departamento de Ciencias Espaciales 7 Teniendo varias descargas, lo cual esta en función de la carga de la nube

33. Departamento de Ciencias Espaciales Distribución Mundial de Descargas Eléctricas Diariamente en el mundo se producen unas 44,000 tormentas y se generan mas de 8,000,000 de descargas

34. Departamento de Ciencias Espaciales Curva de Carnegie según LIS

35. Tank You very much !!!