近地层大气光学湍流的分形和间歇性特征分析

Fractal and intermittency analysis of atmospheric optical turbulence near ground

利用光纤湍流测量系统获得了合肥西郊科学岛上气象观测场内下垫面平坦的水面上方0.48 m、草地上方1.8m和23 m高处的大气折射率起伏的观测数据,采用R/S分析法计算了近地层大气光学湍流的赫斯特指数和分形维数,统计分析了分形维数的日变化特征及概率分布特征.结果表明：对于一天的不同时段,分形维数在一定范围内动态变化,且中午时段相对稳定;在三种下垫面条件下,全天分形维数的值大多在1.3～1.4之间,其最可几概率位于1.35处,从均值来看,草地上方1.8m的分形维数最大,水面上方0.48 m次之,草地上方23 m处最小.最后,初步探讨了近地层大气光学湍流分形维数、间歇性指数和湍流发展程度的相关性.

Atmospheric optical turbulence is fractal. In this article, a high quality fiber optical turbulence sensing system is proposed to obtain time series of air refractive index fluctuations in optical turbulence under three conditions, i.e. , 0.48 meter above water, 1.8 meters and 23 meters above grassland on the Science Island in Hefei. With the time series data the Hurst exponent and fractal dimension of optical turbulence can be estimated using the method of R/S analysis. Diurnal variations and probability distributions of the two parameters are provided and analyzed. The results show that the fractal dimension under the three conditions varies with time in a day and becomes stable at noon. The dynamic range of fractal dimension is from 1.3 to 1.4, and its most probable value is about 1.35. Comparatively, the average value of fractal dimensions at the 1.8 meters above the grassland is the largest, and the value at the 23 meters above the grassland is the smallest. At last, the dependences of fractal dimension and intermittency exponent on the development of boundary layer atmospheric optical turbulence are briefly discussed.