摘要:
选择最好的天文台址放置大口径望远镜а直是天文学家追求的目标.天文台址的选择与近地面层湍流强度大小以及随高度递减的快慢密切相关.与中纬度最好的天文台站相比,南极大陆具有极低的红外天空背景辐射、极低的可降水含量、极低的气溶胶和尘埃颗粒物含量、非常小的光污染、晴天日数多,无疑成为下一代大型光学/红外天文望远镜在地球上寻找地基站址的理想场所.本文建立了光学湍流强度估算方法,第一次对南极泰山站近地面大气光学湍流强度进行估算.模式输入的气象参数是2013年12月30日至2014年2月10日移动式大气参数测量系统在南极泰山站测量的数据,折射率结构常数C2n的估算结果与温度脉动仪实测的C2n进行了比较,并对估算方法进行了敏感性分析.测量结果和分析表明:南极内陆近地面C2n具有明显的日变化特征,夜晚C2n达2×10?14 m?2/3,比白天强,日出和日落时刻附近出现最小值.C2n的模式估算和实验测量的比对表明了模式用来估算南极近地面C2n的可行性.C2n的模式估算和测量差异最大值往往出现在日出和日落时刻附近.由于南极内陆大气大部分时间处于稳定状态,选用不同的结构常数函数估算的C2n值差别不大,0.5 m,2.0 m两高度温差测量精度是影响C 2n估算值的主要因素.
Abstract:
Turbulence intensity in the near-surface layer and its decrease rate with height are closely related to the quality of potential sites. Astronomers have been pursuing a perfect astronomical site to place the large-aperture telescopes. Compared with the best mid-latitude sites, Antarctic plateau inevitably becomes an ideal site for building the next-generation large optical and infrared telescopes, which is because of its low infrared sky emission, low atmospheric precipitable water vapour content, low aerosol and dust content of the atmosphere, and light pollution. In this paper, we establish a model of the atmospheric optical turbulence in surface layer, and use it to estimate C2n at Antarctic Taishan station for the first time. The meteorological parameters of the model input are the data measured by a mobile atmospheric parameter measurement system at Antarctic Taishan station from 30 December 2013 to 10 February 2014. The values of C2n, estimated by the model and measured by a micro-thermometer, are compared. Sensitivity analysis of the estimation method is also carried out. The measurement results and analyses show that C2n obtained at Taishan station has obvious diurnal variation characteristics, with well-behaved peaks in the daytime and nighttime, and minima near sunrise and sunset. C2n obtained in the nighttime is stronger than that in daytime, more specifically, it is on the order of 2 × 10?14 m?2/3. The comparison between model predictions and experimental data demonstrates that it is feasible to estimate C2n in Antarctic by using this model. The biggest differences between C2n values obtained from the model and measurement usually emerge at sunrise and sunset, respectively. Considering the fact that Antarctic atmosphere is in a stable state most of the time, the values of C 2n estimated by different nondimensional structure parameter functions are nearly the same. Thus, the measurement accuracy of air temperature difference from one height to another is the main factor that affects the estimated value of C2n.
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