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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 2008-12 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 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 five 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$\pm$42) spectroscopic clear nights per year is located in the Andes of Venezuela (70$^{\circ}$28'48"W, 9$^{\circ}$5'60"N) at an altitude of 3480 meters. Lower quality regions were found in Sierra Nevada de Santamarta and Serranía del Perijá with (126$\pm$34) and (111$\pm$27) clear nights per year, respectively. Sites over the Andes are identified in Norte de Santander with (107$\pm$23) and in the north-east part of Boyacá with a mean of (94$\pm$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 suggest a possible correlation be tween the lowest percentages observed during the rainy seasons of 2010 and 2011 with positive values of the Southern Oscillation Index.