Ambient conditions and infrared sky brightness in the Chilean Atacama Desert 

<p>The Atacama Desert in the Chilean Andes region is one of the dryest areas in the world. Due to its unique location with stable subtropical meteorological conditions and high mountains, it is an ideal site for the astronomical telescope facilities of the European Southern Observatory (ESO). The special meteorological conditions are continuously monitored at Cerro Paranal (the location of the Very Large Telescope) by measuring various parameters like temperature, pressure, humidity, precipitable water vapour (PWV), wind speed and direction, and sky radiance and bolometric sky temperature, respectively, the latter being crucial for astronomical observations in the thermal infrared regime. ESO operates several site monitoring systems for that purpose, e.g. the ESO MeteoMonitor, the Differential Image Motion Monitor (DIMM) and a Low Humidity And Temperature PROfiler (L-HATPRO) microwave radiometer providing detailed water vapour and temperate profiles up to a height of 12km in various directions.&#160;</p> <p><br />We have assembled all available data for a period of 4.5 years (2015-07-01 through 2019-12-31) and created a unique data set from it. This period also covers the strong El Ni&#241;o event at the end of 2015. In this poster we present statistical results on the overall conditions and trends, and compare our measurements of the nocturnal sky brightness with an empirical model as function of the ambient temperature, PWV and zenith distance.</p>