Identification of Potential Sites for Astronomical Observations in Northern South America

In this study, we describe an innovative method to determine potential sites for optical and infrared astronomical observations in the Andes region of northern South America. The method computes the clear-sky fraction (CSF) from Geostationary Observational Environmental Satellite (GOES) data for the years 2008-2012 through a comparison with temperatures obtained from long-term records of weather stations and atmospheric temperature profiles from radiosonde. Criteria for sky clearance were established for two infrared GOES channels in order to determine potential sites in the Andes region of northern South America. The method was validated using the reported observed hours at the Observatorio Nacional de Llano del Hato in Venezuela. Separate CSF percentages were computed for dry and rainy seasons for both photometric and spectroscopic night qualities. Twelve sites with 5-year averages of CSF for spectroscopic nights larger than 30% during the dry seasons were found to be suitable for astronomical observations. The best site with (220 +/- 42) spectroscopic clear nights per year is located in the Andes of Venezuela (70 degrees 2848W, 9 degrees 560N) at an altitude of 3480 m. Lower quality regions were found in Sierra Nevada de Santamarta and Serrania del Perija with (126 +/- 34) and (111 +/- 27) clear nights per year, respectively. Sites over the Andes are identified in Norte de Santander with (107 +/- 23) and in the north-east part of Boyaca with a mean of (94 +/- 13) clear nights per year. Two sites at low latitude located in Ecuador with more than 100 clear nights per year and with similar seasonal CSF percentages were also identified. Five-year evolution suggests a possible correlation between the lowest percentages observed during the rainy seasons of 2010 and 2011 with positive values of the Southern Oscillation Index.