Atmospheric aerosol typical behavior at the proposed Cherenkov Telescope Array Argentinean sites in the Andes range, for the detection of ultraenergetic cosmic gamma photons

RUBÉN D PIACENTINI; MARTÍN FREYRE; MARÍA ISABEL MICHELETTI; BEATRIZ GARCÍA; GRACIELA M SALUM; JAVIER MAYA; A. MANCILLA

Rio de Janeiro

Conferencia; The 33rd International Cosmic Ray Conference (ICRC2013); 2013

International Union of Pure and Applied Physics (IUPAP)

Aerosols from natural and antropogenic sources are one of the atmospheric components that have the largest spacial-temporal variability, depending on the type (land or ocean) surface, human activity and climatic conditions (mainly temperature and wind). Since Cherenkov photons generated by the incidence of a primary ultraenergetic cosmic gamma photon have a spectral intensity distribution concentrated in the UV and visible ranges [1], it is of importance to know the aerosol concentration and its contribution to atmospheric radiative transfer. We present results of this concentration measured in typical rather calm (not windy) days at San Antonio de los Cobres (SAC) and El Leoncito/CASLEO proposed Argentinean Andes range sites for the placement of the Cherenkov Telescope Array (CTA). In both places, the aerosol concentration has a peak in the 1-7 µm range of the mean aerosol diameter and a very low total concentration of 0.097µgr/m3 (0.365µgr/m3) for SAC(CASLEO). The data were collected the days 15/Dec/2012(27-28/Dec/2012) for the first(second) place with a GRIMM aerosol spectrometer, who determines the aerosol concentration at a given diameter (0.22-32µm range) with a laser technique. The attenuation of Cherenkov photons by aerosols is described by the Aerosol Optical Depth (AOD) for a given wavelength. Consequently, we present AOD values for each CTA [2-6] proposed place, derived with the improved Deep Blue algorithm, from data measured by SEAWiFS instrument on board of SeaStar/NASA satellite. They have very low mean values, determined for the 1998-2010 period, AOD(550)SAC=0.026±0.011 and AOD(550)CASLEO=0.030±0.014. Also, we introduce the spectral (380 nm) solar irradiance as a test in these sites of the tropospheric (0-about 15 km height) UV atmospheric transmittance. This irradiance was measured by OMI/KNMI (The Netherlands) instrument on board of AURA/NASA satellite. We conclude that both Argentinean places have excellent sky quality with respect to the aerosol content.