Turbulent Structure Of Boundary Layers As Revealed By Wind Profiler

The atmospheric boundary layer is an important bridge for the exchange of momentum,heat and water vapor between the underlying surface and the free atmosphere.The vertical transport of turbulence is the main process in the boundary layer.The study of the turbulence characteristics in the boundary layer,especially its vertical distribution,is an important direction for the study of boundary layer meteorology.Wind profile radar is a new type of boundary layer detection radar,with high temporal resolution and continuous observation characteristics.In this paper,the turbulence characteristics of the boundary layer in the boundary layer are studied by using the data of the wind profile in the southeastern China from June to August in 2015,combined with the characteristics of the underlying surface of the site,and the boundary layer turbulence in the clear sky and cloud.The paper can provide an observation basis for assessing and improving the numerical model boundary layer parameterization.Based on the physical mean of the vertical velocity standard deviation and the vertical velocity skewness,the combination of the two can explain the intensity of the turbulence in the complex boundary layer and the main physical factors that affect the turbulence.The main conclusions of the paper are as follows:1)Through the cases and statistics,the characteristics of the boundary layer turbulence in the sunny days are studied.It is found that the standard deviation of the vertical velocity has obvious diurnal variation characteristics,and the maximum value is reached from 12 noon to 16:00 pm.The vertical velocity skewness is also found having obvious diurnal variation characteristics.After the sunrise,the positive value appears from the bottom of the boundary layer,and emergence of positive skew value in the afternoon can be developed to more than 1400 meters.These characteristics are in accordance with the characteristics of the occurrence and development of turbulence in the typical convective boundary layer.The turbulence is developed from bottom to top and reaches the mixed boundary at the boundary layer,and the turbulence intensity is the strongest.The vertical profile of the vertical velocity skew in the flat terrain,in sunny days(such as Zengcheng),presented increases with height at the bottom,and at the upper layer has little change,which is consistent with the previous research results(Lenschow et al.2012).At this time,the vertical velocity standard deviation,on average,presents the maximum at 1/3 to 1/4 of the thickness of the lower boundary layer,and then decreases with height.2)Similarly,the characteristics of the turbulence in the boundary layer with cloud cover(no precipitation)are studied.The study distinguishes between low clouds and other kinds of clouds covering different situations.In the case of low clouds,the sky is covered by large amount of clouds(stratigraphic clouds),and the solar radiation received in the daytime surface is obviously weakened,and the turbulence is weaker than the turbulence intensity of the convective boundary layer.The standard deviation is 0.7m/s on average;The vertical distribution of the skewness can clearly see the large negative area near the cloud,and the development of the negative area can reach the ground.It shows that the development of turbulence in the boundary layer is mainly affected by the influence of cloud radiation cooling From the top-down developmental characteristics,which is consistent with the results of Hogan et al.(2009)based on Doppler lidar research.3)In addition to the typical sunny convective boundary layer,turbulence development at the boundary layer in the case of cloud cover shows obvious surface-heating-driven,top-down development mechanism.In addition,about 66.4% of the boundary layer turbulence development presents more complexity.This complexity comes from the influence of local small and medium scale circulation,such as valley wind,sea land wind and so on.For example,Yichun is located in the basin,Zhuhai is located by the sea.At night,the standard deviation of vertical velocity above 1000 m in the basin grows,and the skewness of the corresponding vertical velocity is positive,indicating the upward transport of turbulent kinetic energy.In this case,The generation of turbulence requires further elaboration of more detailed observations.4)The analysis of the characteristics of the turbulence at the boundary layer based on the wind profiler radar shows that the top cloud-radiation interaction in the boundary layer and the boundary layer is an important process for the occurrence of turbulence and should be considered in the parameterization of the model.At the same time,the influence of the local small and medium scale circulation on the boundary layer turbulence at the present stage is limited by the resolution of the model and should not be taken seriously.