Atmospheric considerations for CTA site search using global models

TL;DR

This study evaluates atmospheric conditions at potential CTA sites using global models, focusing on cloud cover, wind, and air mass trajectories to identify the most suitable location for gamma-ray observations.

Contribution

It applies validated atmospheric models to compare candidate sites, providing a comprehensive assessment of atmospheric suitability for CTA site selection.

Findings

Namibian site has the most favorable atmospheric conditions.

One Argentine site is unsuitable due to poor atmospheric quality.

Cloud cover and wind speed are critical factors in site evaluation.

Abstract

The Cherenkov Telescope Array (CTA) will be the next high-energy gamma-ray observatory. Selection of the sites, one in each hemisphere, is not obvious since several factors have to be taken into account. Among them, and probably the most crucial, are the atmospheric conditions. Indeed, CTA will use the atmosphere as a giant calorimeter, i.e. as part of the detector. The Southern Hemisphere presents mainly four candidate sites: one in Namibia, one in Chile and two in Argentina. Using atmospheric tools already validated in other air shower experiments, the purpose of this work is to complete studies aiming to choose the site with the best quality for the atmosphere. Three strong requirements are checked: the cloud cover and the frequency of clear skies, the wind speed and the backward trajectories of air masses travelling above the sites and directly linked to the aerosol concentrations. It was found, that the Namibian site is favoured, and one site in Argentina is clearly not suited. Atmospheric measurements at these sites will be performed in the coming months and will help with the selection of a CTA site.