Site Test for Infrared Solar Tower in Yunnan

This paper describes the history of site tests for solar optical observations in Yunnan.The site test for the infrared solar tower (IST) in Yunnan began from 1996,and consisted of 3 phases:the preliminary site survey,comparison observation and the observation at the fixed stations (with S-DIMM).The best site is finalized at Lao Ying Di,a small peninsula on the bank of Fuxian Lake,Cheng Jiang county. The site for the IST station at Lao Ying Di is chosen following the comparison observation with SDIMM for over one year at two final near-water sites.The two sites are picked out from 7 sites near water and 8 sites in mountain areas with visual observation by using an 89mm Questar telescope after on-site survey over 40 candidate locations in Yunnan. The IST station is about 68 km form Kunming,the capital of Yunnan province.The average sunshine time is 2200 hours annually at the site.The yearly mean R0 observed with SDIMM characterizing the solar seeing is 12.3cm,with a moderate value of 11.5cm,corresponding to a resolution of 1";the maximum R0 reaches to 42 cm,corresponding to a resolution of 0.3".The R₀ below 5 cm accounts for less than 10 per cent of the total samples.The rate of recurrence of the measured wind speed,less than 5m/s is 90%,and that of the wind speed at 6-10m/s is about 6%.The strong wind,at a speed higher than 15m/s,occurs only 3 times in a year.The yearly mean relative humidity is 75%,and the average water vapour in the atmosphere is 11 cm annually.