Characterization of atmospheric properties at the future sites of the\n Cherenkov Telescope Array

Abstract

Advanced knowledge of the detailed atmospheric properties of both the future\nsites of the Cherenkov Telescope Array is essential in preparation of the\narrival of the first scientific data. Meteorological variables are studied\nusing a dedicated characterization station installed at the southern site in\nChile and a wealth of data from existing observatories around the northern site\non the La Palma island. Campaigns using radiosondes launched on balloons are\nforeseen to complement these data in the near future. Cloudiness during the\nnight has been continuously monitored at both sites for several years using\nAll-sky Cameras which assess the presence of clouds based on detection of\nstars. The integrated aerosol optical depth over the southern site has been\nmeasured using a Sun/Moon Photometer since 2016 and the small robotic FRAM\ntelescope since 2017; identical instruments have been deployed at the northern\nsite in autumn 2018. Also in October 2018, the ARCADE Raman lidar (RL) has\nstarted to take measurements on routine basis at the northern site, providing\ndata on the vertical profile of the aerosol optical properties (i.e.,\nextinction and scattering) and of the water vapour mixing ratio. We present the\ndata currently available from these instruments from both sites with emphasis\non characteristics important for the (future) operation of Imaging Atmospheric\nCherenkov Telescopes.\n