Atmospheric Transparency and Precipitable Water Vapor at the Gaomeigu site in Lijiang

Atmospheric aerosol and precipitable-water affect the quality of measurement of an astronomical telescope and its imaging system. A ground-based solar photometer made by the Anhui Institute of Optics and Fine Mechanics was used to measure solar irradiance in clear and cloudless weather from October 2010 to May 2011 at the Gaomeigu site, Lijiang, Yunnan Province, China. We obtained the measurements of the aerosol optical thickness (AOT, which represents the atmospheric transparency), Ångström index, and the precipitable water vapor(PWV) in clear and cloudless weather. We subsequently analyzed the diurnal and seasonal variations of the three parameters. Our analysis shows that there are four diurnal variation patterns for AOT or PWV. It also shows obvious and consistent seasonal variations of these two parameters. The two parameters both reach the minima in winter, remain small in autumn, and become large in spring. Statistically, the values of AOT are between 0.01 and 0.1, those of Ångström index are between 0.8 and 2.0, and PWV values are between 0.04 cm and 0.5 cm. The value distributions of all the parameters are basically Gaussian. In summary, AOT and PWV at the Gaomeigu site are at low levels in clear and cloundless weather. This indicates that the atmosphere there is clean and transparent, and the particles in the air are mostly small. The site is thus appropriate for astronomical observation.