Climatological Study for the Cherenkov Telescope Array North Site at the Canary Islands I: Temperature, Precipitation, and Relative Humidity

Abstract

We obtained climate normals over a period of 10 years (2003–2012) at Izaña (2395 m), Tenerife (Spain) with the aim of characterizing the mesoscale climate conditions governing the two astronomical observatories in the Canary Islands: Teide Observatory, located on the summit of Izaña and Roque de los Muchachos Observatory (ORM), approximately 140 km away, on the island of La Palma. Both sites are at the same height (≈2300 m) and share very similar regional climatological conditions. The study was carried out as part of the site selection campaign for the Cherenkov Telescope Array (CTA) in the northern hemisphere, which was finally installed at the ORM. We used long-term and high-quality climate data series recorded by the Centro de Investigación Atmosférica de Izaña (CIAI) at the Izaña Atmospheric Observatory (IZO; WMO#60010). In this paper, we analyze the temperature (central tendency, maxima, minima, and ranges), precipitation (intensities per hour and daily, monthly, and yearly cumulative), and relative humidity. The precipitation data are divided into liquid, snow, and hail. All the results are presented in triplicate, covering the whole series, nighttime, and daytime. The results show a smooth temperature profile with sporadic but moderate extremes, a low daily (24 h) temperature range (median 7.1 °C), and extremely low nighttime temperature range (median 2.7 °C). Rainfall is very rare and sporadic (287 mm a−1), with low intensities. The relative humidity is also low (median 29% and 25th percentile 15%) and follows the precipitation cycle. These results confirm the stability and optimal conditions required to fully operate CTA and other astronomical facilities. The requirements specified in the CTA project documentation are fulfilled.