基于多普勒激光雷达的边界层内湍流参数估算

Estimation of Turbulence Parameters in Atmospheric Boundary Layer Based on Doppler Lidar

2019年10月,使用相干多普勒测风激光雷达在深圳杨梅坑地区进行风廓线等观测。结合标准大气模型、温度日变化模型和地面气象站数据,估算了晴朗天气下边界层内大气折射率结构常数C_(n)^(2)和湍流动能耗散率ε。根据时间-高度垂直剖面,分析了时空变化特征,研究了各参数变化对C_(n)^(2)的具体影响。折射率结构常数C_(n)^(2)与垂直速度方差σ_(a)^(2)有较强的相关性,相关系数-般在0.7以上。在白天湍流充分混合发展的情况下,湍流动能耗散率ε与C_(n)^(2)相关系数一般达到0.5以上,C_(n)^(2)、σ_(a)^(2)及ε的相关性体现了湍流在水平和垂直两个方向变化的一致性。这表明在缺乏温度压强数据情况下,基于温度压强模型估算C_(n)^(2)是可行的。基于误差分析,温度梯度对C_(n)^(2)的贡献率达28.84%.温度对C_(n)^(2)的贡献率达30.12%,这要求在计算过程中尽量获取准确的温度廓线。结果对研究深圳地区地气系统能量、物质交换和天气变化等具有借鉴意义。

Objective In the atmospheric boundary layer,studying the formation and development of turbulence is of significant interest to numerical weather prediction,atmospheric dynamics,mechanical structure safety of wind power equipment,and aviation safety.The refractive index structure constant C_(n)^(2)and turbulent energy dissipation rateεare commonly used parameters for studying the intensity of atmospheric turbulence.Traditional observation methods rely on meteorological elements,such as temperature,pressure,humidity,and wind field obtained from radiosondes.Micro-temperature sensors,ultrasonic anemometers,and wind profile radars,combine with corresponding methods to obtain atmospheric turbulence parameters.A new observation method based on lidar observation of atmospheric turbulence parameters has been widely studied.Compared with traditional observation methods,lidar can detect vertical profiles round the clock and high temporal-spatial resolution.In this study,we present the estimation of C_(n)^(2)andεbased on the coherent Doppler wind lidar observation data with second-level time resolution,combined with the temperature and pressure diurnal variation model.Besides,the vertical change profile of C_(n)^(2)round the clock is presented and compared with the vertical velocity varianceσ_(a)^(2).We believe that the proposed methods and estimation results can be useful for studying the characteristics of turbulence parameters in the boundary layer,the energy exchange of the land-atmosphere system,and transportation and diffusion of pollutants in coastal urban areas.Methods First,the wind speed data observed by lidar with a signal-to noise ratio of less than 8 dB and observation height below 60 m are eliminated.The meridional wind U and zonal wind v are calculated using the wind speed data after quality control.Then,the US standard atmosphere model is used to simulate changes in temperature and pressure at different altitudes.The GOT01_0 temperature diurnal change model is used to simulate the diurnal temperature change.The potential temperature is calculated based on the empirical rela tionship between temperature,pressure,and potential temperature.Finally,the refractive index structure constant C_(n)^(2)is estimated using the method proposed by Tatarski.By estimating the velocity structure function,the turbulent energy dissipation rate is estimated using the outer scale L_(0)and the vertical velocity standard deviationσ_(a)^(2).The turbulent energy dissipation rateεand the vertical velocity varianceσ_(a)^(2)representing the vertical component of the turbulent kinetic energy were compared with C_(n)^(2)to characterize that it is feasible to estimate C_(n)^(2)based on the temperature and pressure model.Besides,the influence of each variable required to calculate C_(n)^(2)on the calculation result is investigated based on the theory of error analysis to guide for further in-depth research.Results and Discussions The magnitude of C_(n)^(2)is between 10^(-16)and 10^(-13)m^(-2/3).It is mainly concentrated on.10^(-16)m^(-2/3),and the refractive index structure in a dry and clean atmosphere in the order of 10^(-18)to 10^(-13)m^(-2/3)is consistent.As the height increases,C_(n)^(2)gradually decreases,indicating that the turbulence intensity decreases as the height increases.The strong turbulence is mainly concentrated below 1 km,and the turbulence intensity is weaker at 1 to 1.5 km,but this trend is not absolute;however,the strong turbulence can reach 1.5 to 2 km(Fig.3).Except for October 18,the other observation days showed a sudden increase in C_(n)^(2)between October 17 and 21,and the height rose from 500 to 900 m.It may be due to strong turbulent uplift caused by changes in ground thermal radiation after temperature attenuation and may also be related to the conversion of sea and land wind.The daily variation of C_(n)^(2)near the ground presents an obvious“Mexican hat”shape,i.e.,during the day,C_(n)^(2)is higher than that at night,which is also reflected in 360 m.As the height increases,the hat-shaped diurnal varia tion gradually disappears,and the diurnal variation of C_(n)^(2)at 720 m presents random fluctuations(Fig.5).σ_(a)^(2)and C_(n)^(2)have a strong correlation,and the correlation coffficient is above 0.7,indicating the consistency of turbulence in the vertical and horizontal directions.Besides,the correlation decreases when the surface temperature at night decreases.There is a certain correlation betweenεand C_(n)^(2),when the turbulence is fully mixed and developed during the day;the correlation coefficient is above 0.5.The dynamic range of C_(n)^(2)estimated by simulated temperature and pressure is smaller than that estimated by GMAO meteorological data of CALIPSO data(Fig.8),which is mainly caused by the fact that the standard atmospheric profile cannot reflect the randomness of instantaneous temperature change.Conclusions In this study,the wind profile observation data of the coherent Doppler wind lidar in the Yangmeikeng area of Shenzhen are used,combined with the standard a tmosphere model,the diurnal temperature model,and the data from the ground weather station.The atmospheric refractive index structure constant C_(n)^(2)and turbulent energy dissipation rateεin the atmospheric boundary layer under clear weather are estimated.The characteristics of temporal and spatial changes are analyzed according to its time height vertical profile.Besides,we investigated the specific effects of changes in various parameters on C_(n)^(2).The high correlation between C_(n)^(2)andσ2 estimated based on the horizontal wind showed that the turbulent motion is isotropic.The estimation based on temperature and pressure models is feasible in the absence of measured temperature and pressure profiles.Compared with the calculation results of GMAO standard meteorological data,the estimated C_(n)^(2)has a smaller dynamic range,which is due to the absence of instantaneous changes in the simula ted temperature profile.To further accurately investigate the changes in turbulence parameters in the Shenzhen area,long term joint observations with various equipment must guide the study of atmospheric pollutant transport and diffusion and weather changes in the Shenzhen area.