抚仙湖太阳观测和研究基地知识库

We describe a solar seeing monitor used for the site testing for the 4 meter US Advanced Technology Solar Telescope and the 1 meter Yunnan Observatory Solar Telescope. It has two parts: a solar Differential Image Motion Monitor (S-DIMM) and a linear array of 6 solar scintillometers (SHABAR = SHAdow BAnd Ranger). The results obtained by both methods are compared on the basis of observations obtained in February 2002 at the Yunnan Observatory Fuxian Lake solar station. Analysis showed that these two ways of measuring the Fried parameter give consistent results. We confirm earlier observations that showed that the boundary layer seeing over lakes is strongly suppressed. The amount of this boundary layer seeing depends on the temperature difference between lake and air and on the wind velocity. We have also carried out seeing observations along a 9.15 km horizontal path across the lake. The Cn2 values derived from these is consistent with the solar observations. They confirm the dependence of Cn2 on the lake-to-air temperature difference. From the SHABAR we find a typical scale height for the boundary layer seeing of 20 meters and from inter-comparison of the S-DIMM and SHABAR observations we derive an outer scale of turbulence of about 50 meters.