El Roque de Los Muchachos site characteristics

Abstract

Context. In this paper we present an analysis of wind speed, wind direction, relative humidity and air pressure taken at Telescopio Nazionale Galileo (TNG), Carlsberg Automatic Meridian Circle (CAMC; now called Carlsberg Meridian Telescope) and Nordic Optical Telescope (NOT) at Observatorio del Roque de LosMuchachos, in the Canary Islands. Aims. Data are also compared in order to check local variations and both long term and short term trends of the microclimate. Furthermore, influence of wind speed on the astronomical seeing is estimated to the aim to better understand the influence of wide scale parameters on local meteorological data. Methods.The analysis is done using a statistical approach. From each long series of data we compute the hourly, daily and monthly averages. A particular care is used to minimize any effect due to biases in case of missing of data.Wind direction is estimated by the annual percentage of the time in which the wind come from fixed directions. Results.We found that relative humidity presents a negative correlation with temperature and pressure, while pressure is correlated to the temperature. The three telescopes show different prevailing wind direction, wind speed, relative humidity and air pressure confirming differences in localmicroclimate.We found that seeing deteriorates when wind speed is lower than 3.3ms−1. Comparison in terms of wind speed and high relative humidity (> 90%) shows that TNG seems to have optimal observational conditions with respect to CAMC and NOT. Air pressure analysis shows that ORMis dominated by high pressure, that means prevailing stable good weather, as is to be expected from anticyclonic conditions. Finally, short time variations of pressure anticipate temperature variations tipically by 2-3 hours, this property vanishes in time scales higher than some hours and disappear in longer time scales.