Density profile characterization and modeling at Paranal and Armazones 2k sites

Abstract

Abstract. The Cherenkov Telescope Array (CTA) in the southern hemisphere will be installed at Armazones 2k site in northern Chile. Scarce atmospheric observations are available in the region, particularly radiosonde data. This study analyzes radiosondes launched at Paranal observatory, located at about 21 km from the CTA site, from 24 October and 4 November 2011, to understand the behavior of density in the atmosphere near the CTA site. High-resolution numerical simulations with the Weather Research and Forecasting (WRF) model are validated with Paranal radiosondes to quantify its ability to represent the atmospheric conditions in the region. In addition, the seasonal and diurnal evolution of atmospheric density at the CTA site were studied during 2011 using the high-resolution weather forecasts from the WRF model.

Site Characterization of the Northern Site of the Cherenkov Telescope Array

“…and in the tropopause. The latter has also been observed in the South [17]. At about 15 km, the strongest relative differences between Summer and Winter is observed, with an average seasonal variation amplitude of about 7% (see Fig.…”

“…A spatially better resolved WRF model [16], as employed by J. Marín in these proceedings [17], has not yet been tried, however the European ECMWF 11 is currently being tested, yielding similar or even better results, while the IG2 model [19] does not agree well with instantaneous MAGIC data at these altitude ranges, at least what concerns the temperature profiles. Similarly, the NRLMSISE-00 model [20], although very accurate above 20 km a.s.l., is not able to resolve all tropospheric temporal variations and can show deviations from the GDAS model of up to 10%.…”

Overview of Atmospheric Simulation Efforts in CTA

“…To get this information CTA plans to use several instruments measuring the atmosphere -Raman LIDARs, the FRAM telescope, All-Sky-Cameras, Ceilometers, sun and moon photometers and radiosondes (see e.g. [13], [14], [15] or [16], for an overview see [3]). …”

CTA Atmospheric Calibration

“…The assumed error of only 2-3% rms induced by this choice resulted to never limit their overall systematic uncertainty, by a factor of several times higher [5,6]. Whether such a statement is still true for the CTA, is currently being investigated [37,38]. The difference is not only due to the stricter requirements on the CTA's accuracy, but also to its wider coverage of gamma-ray energies.…”

“…37]. On the other side of the spectrum, very low energy showers develop in an around the tropopause where relative density variations, and their uncertainties, are largest [37].…”