Research On Coherent Structure Characteristics Of Atmospheric Turbulence In Typical Areas Of China

The coherent structure of atmospheric turbulence is an organized large scale vortex structure in turbulence,which plays an important role in the formation,development and evolution of turbulence.The material exchange,energy and momentum transport caused by coherent structure of atmospheric turbulence are of great significance for studying atmospheric dynamics.The parameter of the light wave is destroyed when the laser is transmitted in the turbulent atmosphere,which causes a series of atmospheric turbulence effects and seriously restricts the application of the photoelectric engineering.This restriction is not only reflected in the turbulence intensity,but also on the turbulence scale.Therefore,the study of coherent structure characteristics of atmospheric turbulence is of great theoretical value and important application value.A method based on frequency domain wavelet analysis is proposed to study the coherent structure characteristics of atmospheric turbulence in this paper.According to the principle of energy maximum,the main scale of coherent structure is identified and the coherent structure waveform is extracted by the reconstruction formula.Combined with the method of spectral analysis,the reconstruction performance is statistically analyzed.The method is more persuasive compared with traditional method.We use an atmospheric parameter observation system near-surface to study the coherent structure characteristics of the near ground turbulence in the Dunhuang area,and use the wind profiling radar to study the coherent structure characteristics of the turbulence in the upper atmosphere in the Hefei area,and get the following research results:(1)The research shows that reconstruction of coherent signal waveform with quasi periodic motion,which reflects a middle scale movement of the existing original pulse signal,and their waveforms coincide well with each other.The time and scale of the wavelet coefficients can explain the multiscale of the turbulence well,and reflect the evolution of the coherent structure of the turbulence.(2)Based on the statistical analysis of the main dimensions of the coherent structure of the near surface atmospheric turbulence in Dunhuang area,we find that the main scale approximation of the coherent structure satisfies normal distribution.Using statistical method to analysis reconfiguration deviation,which proves the rationality and accuracy of reconstructed coherent signal.The spectral analysis of the turbulence signal and the coherent signal shows that the power spectrum of the turbulence signal satisfies the "-5/3 law" of Kolmogorov,and the power spectrum of the coherent signal deviates from the "-5/3 law" of Kolmogorov and the spectral power ratio is near the-2.0.The period and scale ratio of coherent structure obey normal distribution,whose value ranges from 3.30 to 4.10.which indicates the intermittency of turbulence.(3)Using the wind profile radar data to study the coherent structure characteristics of the turbulence in the upper atmosphere in the Hefei area.It is found that the coherent structure of high altitude turbulence has several main scales,which indicates that turbulence is a vortex structure of multi-scale motion.The large scale coherent structure can control the turbulence indirectly by controlling the small scale turbulent coherent structure,and indirectly proves the passing of the turbulent eddy energy.The main scale of the coherent structure of turbulence in the upper atmosphere is close to 1 hour,but there may be a structure of less than 30 minutes in the atmosphere near the top of the atmospheric boundary layer between 1-2km.As the height increases,it may be due to the insufficient development of the high altitude turbulence compared with the boundary layer,and there will be the situation of the smaller main scale or turbulent vortex breakage.