Laboratory Tank Study On The Entrainment Parameterization And The Optical Turbulence Characteristics Of The Atmospheric Boundary Layer

In this paper, flat-underlying-surface convective boundary layer is simulated in laboratory simulation tank. Using the simulation result and field measurement data, by analyzing the structure characteristics of the entrainment layer, the parameterizations of entrainment process and the characteristics of optical turbulence are studied.The entrainment process plays a key role in the structure of atmospheric boundary layer, and is the main mechanism of transmission of mass and energy between the mixed-layer and the free atmosphere aloft. However, this process can not be solved explicitly in general circulation or mesoscale models, thus parameterizations are needed, including the parameterization of entrainment flux,entrainment rate and entrainment layer depth. However, the existing parameterization schemes for entrainment rate and entrainment layer depth are faulty, thus the simulation and field measurement data can't be consummately explained. In this paper, by using data from tank simulation and field measurement, the entrainment paramterizations are studied. A new Richardson number scheme is obtained and based on which, new paramerization schemes for entrainment rate and entrainment layer depth are achived. The existing data can be well explained by new parameterization schemes. The main results are summarized as follow.(1) Using tank simulation data, paramterization ratios of entrainment flux are stastically studied; the analysis of the simaltated boundary layer shows the simulation is close to the real atmosphere; the further comparison study between tank simulation and numerical simulation show good agreement with each others, which validates the reliability of tank simulation.(2) By analysis the structure of entrainment layer, a simplified model of the entrainment layer and a new temperature jump scale of entrainment layer are introduced, subsequently a new Richardson number scheme and a new paramterization of entrainment rate. The new Richardson number, embodying the influences of the strength of inverse layer and the free atmosphere stratification, has consummate physical meaning; the new paraterization scheme has a good agreement with tank simulation results.(3) The insufficiencies of the existing paramterization schemes for entraiment layer depth are analyzed. And then, by using the simplified model of entrainment layer, a new parameterzation scheme is introduced. The new scheme has a good agreement with tank and field data. The comparison between the existing schems shows, the new scheme is more applicable under complex conditions in real atmosphere.Because of the paucity of reliable measurements in the interfacial layer, the temperature structure of the mid-and upper- region of atmospheric boundary is not well understood. In this paper, the details of temperature structure in the CBL are investigated visual observations of penetrating the tank using the collimated laser beam. By using the collected beam patterns, the optical turbulence characteristics and the influence of large scale structure on temperature structure parameter are studied. The main results are summarized as follow.(1) The inhomogeneity of Atmospheric boundary layer is studied using beam patterns, which gives a further review on the charateristics of atmospheric boundary layer, especially the entrainment layer. Studies show, the mixed layer is quite homogeneous in horizontal direction, and a little inhomogeneous in vertical direction; the inhomogeneity of entrainment layer relies on the convective conditions.(2) Using beam patterns, the behavior of temperature structure in convective boundary layer is studied. Results show, Wyngaard's mixed-layer scaling law has a good validity in tank data; however, the entrainment layer scaling expression is not reliable under unstable condition. Based on the results of simulation and filed measurement, a new dimensionless expression is introduced.(3) Based on the aforementioned studies, the entrainment layer structure of entrainment layer and the characteristics of large scale structure are discussed. By mutli-scale decomposition of log-intensity using wavelet transform method, the charateristics of structures at different scales are analyzed, which introduces a large scale decompostition method for log-intensity. Thus, the temperature structure paremter can be decomposed into the contribution of large scale structures and small scale structures. By normalising each part, the behavior of the temperature structure parameter in the entrainment layer is well explained. And a new scaling scheme is introduced, which can explain the behavior of the temperature structure parameter profile in the entrainment layer.(4) Based on the mixed-layer scaling law of the temperature structure parameter, a new optical method to estimate turbulent variables in tank simulation is introduced, which is more real-time and reliable than commonly-used heat-flux-profile method.