El Roque de Los Muchachos Site Characteristics. I. Temperature Analysis

Abstract

ABSTRACTWe present an analysis of temperature taken at two telescopes located at the Observatorio del Roque de Los Muchachos, in the Canary Islands. More than 20 years of measurements at the Carlsberg Automatic Meridian Circle (CAMC; now called the Carlsberg Meridian Telescope) are included. Analyses of data from the Telescopio Nazionale Galileo (TNG) and CAMC are compared in order to check local variations and long‐term trends. Furthermore, the temperatures at different heights are correlated with the quality of astronomical seeing. We consider a correlation between the North Atlantic Oscillation (NAO) Index and annual downtime with mean annual temperatures. The final aim of this work is to better understand the influence of wide‐scale parameters on local meteorological data. The analysis is performed using a statistical approach. From each long series of data, we compute the hourly averages and then the monthly averages in order to reduce the short‐term fluctuations due to the day‐night cycle. Particular care is taken to minimize any effect due to biases due to missing data. Finally, we compute the annual average from monthly averages. The two telescopes show similar trends. There is an increase in temperature of about 1.0°C per 10 yr from the annual means, and in addition, the annual minimums increase more rapidly than the maximums. We find that a positive NAO Index reduces the increase of temperature and accelerates the decrease. Moreover, there is no evidence that a positive NAO Index corresponds to a lower number of nonobservable nights. Finally, seeing deteriorates when the gradient of temperatures between 2 and 10 m above the ground is greater than −0.6°C.