Abstract

" Because of the high transparency in infrared wavelength, Co. Chajnantor (5,640m altitude) at Atacama, Chile, is one of the most promising sites for infrared astronomy in the world. For evaluating the site condition quantitatively we carried out weather and cloud emissivity monitoring campaign from April 2006 to April 2007. The ground-level condition such as wind direction, wind speed, air temperature, and humidity was monitored by a weather station installed at the summit. Cloud emissivity was estimated by mid-infrared sky images taken by a whole-sky infrared camera every five minutes for 24 hours a day, every day. Results are summarized as followings. 1) The weather condition at the summit is slightly harsher than the condition at the Pampa la Bola plateau. Maximum speed of the wind is 35m/s, and minimum temperature is about -10 degree. 2) Fraction of ""clear+usable"" weather (which is defined as the cloud emissivity < 10%)"" is 82% in a year. The fraction decrease to 40-50% on Bolivian winter season, and increases to over 90% from April to July. This is comparable or even better than the other astronomical sites. "