| Cloud precipitation process is an important part of the water cycle,which has an important impact on weather,climate,weather modification and Atmospheric chemistry.It is also one of the most uncertain factors in weather climate models,especially cloud microphysical processes and turbulence in clouds.At the same time,the interaction mechanism of turbulent processes in cloud microphysical processes such as condensation,collision and growth of cloud droplets,clustering,and broadening of cloud droplet spectra is still unclear.However,the insufficient accuracy and scale of cloud microphysical parameters and turbulence observation methods hinder a deeper understanding of cloud precipitation processes.The paper focuses on the observation needs of turbulence in clouds and conducts experimental research on the analysis method and analysis method of cloud turbulence using cloud microphysical parameter fluctuations.The main research includes:based on the current observation and analysis methods in the field of cloud turbulence,the turbulence theory,cloud microphysical parameter theory,and digital holographic interference theory,combined with the method of analyzing cloud turbulence using cloud microphysical param eter fluctuations,We conducted field experiments to detect the diameter of cloud droplets and conducted research on the distribution of cloud microphysical parameter fluctuations and the corresponding turbulence energy spectrum slope of cloud microphysical parameters.We obtained the distribution patterns of cloud microphysical parameter fluctuations in different environments and the corresponding turbulence energy spectrum slope of each cloud microphysical parameter.In order to improve the accuracy of the research,it is necessary to improve the algorithms used in this study.In order to eliminate noise caused by factors such as power frequency interference and weather changes,preprocessing operations are required for analyzing pulsation data used in cloud turbulence.The overall idea of outlier removal in preprocessing is analyzed,which is to use the Grabbs criterion for removal,use past experimental data,and observe the outlier removal results at different parameters based on the sampling frequency of the experimental system to obtain the best algorithm for outlier removal,By analyzing the number of iterations,the number of data n in the sliding window is determined to be 7,and the corresponding Grabbs critical value is obtained.Finally,outliers are eliminated through the formula of the Grabbs criterion.In order to make the trend of turbulence energy spectrum most obvious and the energy leakage minimum,the algorithm for turbulence energy spectrum is analyzed,and different cloud microphysical parameters plus different Window function are used for comparison during Fourier transform.Due to the small low-frequency energy leakage and the minimum 0.03 Hz oscillation in the fastest frequency band of energy transfer,the most suitable Window function is a rectangular window.After determining the required algorithm for research,in order to obtain cloud droplet size data,an external field cloud droplet detection experiment based on coaxial digital holographic interferometry was conducted.The experimental site is located at the top of Mount Liupan in Ningxia.Holographic droplet spectrometer and three-dimensional ultrasonic anemometer are placed on the experimental platform.In order to reduce the impact between the two instruments and detect turbulence with a turbulence scale of 1 m,the distance between the two instruments is 1 m.After obtaining the three-dimensional coordinates and particle diameter of cloud droplets in the sampling space through coaxial digital holographic interference experiments,cloud droplet diameter data and wind speed pulsation data detected by a three-dimensional ultrasonic anemometer are obtained.To obtain the temporal fluctuations of cloud microphysical parameters,it is necessary to calculate the diameter information of cloud droplet particles in each frame of the photo using the cloud microphysical parameter formula.After conducting multiple sets of coaxial digital holographic interference experiments and three-dimensional ultrasonic anemometer experiments for comparison,based on the law that only wind speed changes significantly in the experimental environment,the height of wind speed is used as a symbol to distinguish the experimental environment.Two sets of cloud microphysical parameter pulsation data detected by the holographic droplet spectrometer at different wind speeds(4.04 m/s and 1.20 m/s)are selected and calculated using the holographic droplet spectrometer,Afterwards,conduct subsequent turbulence analysis in the cloud.When obtaining the time series pulsation data of cloud microphysical parameters to analyze the turbulence pulsation data in clouds,the value of the pulsation data distribution research is first introduced,that is,to solve the problem of Reynolds equation unclosed,and three curve fitting methods of Gaussian distribution,extreme value distribution,and Exponential distribution are proposed to study the pulsation distribution,and it is pointed out that because the time series pulsation data distribution does not converge to the Exponential distribution,Therefore,it is abandoned and only Gaussian distribution and extremum distribution are chosen.For the pulsation distribution in different environments,evaluate the difference between the R-squared parameters of the two fitting methods using the same cloud microphysical parameter pulsation.And for temporal pulsation data,kurtosis and skewness are also used to analyze and evaluate it,and the conclusion of the pulsation distribution of various cloud microphysical parameters in different environments is finally obtained.That is,when the wind speed is 4.04 m/s,the average diameter and number concentration R square are greater than 0.98,which conforms to Gaussian distribution,and the water content pulsation conforms to extreme distribution;When the wind speed is 1.20 m/s,the fluctuations of the three cloud microphysical parameters conform to the extreme distribution.In order to investigate the energy dissipation of various cloud microphysical parameter fluctuations over time,turbulence energy spectrum analysis was adopted,and Fourier transform was used to obtain the corresponding turbulence energy spectrum and slope of cloud microphysical parameter fluctuations for quantitative comparison.Finally,the law between the corresponding turbulence energy spectra of each cloud microphysical parameter was obtained,which is in a downward trend and consistent with the characteristics of turbulence energy spectrum,But the absolute slope value is much smaller than the absolute slope value of the turbulent energy spectrum of wind speed fluctuations;When the wind speed is 4.04 m/s,the absolute slope of the average diameter and number concentration turbulent energy spectrum is greater than when the wind speed is 1.20 m/s,but the opposite is true for the water content.The paper combines the development trend of turbulence research in the cloud,based on the basic physical properties of turbulent flow fields and the measurement method of cloud droplets using coaxial digital holographic interferometry technology,proposes the use of fluctuations in cloud microphysical parameters to analyze cloud turbulence,providing data support and technical support for researchers in the field of cloud precipitation physics in scientific research such as the combined effect of gravity and turbulence,cloud generation and dissipation under the influence of turbulence,and entrainment under the influence of turbulence,And provide certain support for research in fields such as artificial precipitation and ensuring water resource security. |
