A Study of Evolution and Dynamics of Urban Atmospheric Mixing-Layer Depth Based on Lidar Data and Numerical Simulation
基于激光雷达遥感和参数化模式研究城市混合层的发展机制

Mixing-layer depth and entrainment zone thickness are extracted from micro pulse lidar data sets measured at Peking University when surface wind is mainly from the south.The estimated values of the normalized entrainment zone depth are plotted versus an entrainment Richardson number,resulting in a good ordering of the data and agreement with the parameterization proposed in a study by Gryning and Batchvarova.The evolution and dynamics of mixing-layer over urban area under simply meteorological conditions are studied using a simple well-mixed boundary layer theory and the entrainment flux ratio(which is often used to simulate entrainment in atmospheric boundary-layer models) with an empirical relationship which is calculated from these two quantities.This ratio is generally believed to be 0.24 under equilibrium conditions,but is highly variable during the morning and evening hours.Regional surface fluxes of sensible heat are retrieved based on a traditional thermodynamic model without mechanical mixture effects from the time series.The cause for differences between retrieval result and actual measurement(with a correlation coefficient of 0.79) are discussed.It is the differences that make the quantification of the parameter B for mechanical turbulence production possible.A value of 3.5 is confirmed from the result of GB91 numerical simulation.Preliminary analysis indicates both convective and mechanical turbulence,which can be interpreted qualitatively by parameters A and B,contribute to the growth process,in which the importance of every parameter can be estimated when the difference in retrieved surface fluxes of sensible heat is growing rapidly.In this study,five experiments are available for evaluating the simulation of the growth of the mixed layer.When the model adopts the effect of vertical motions induced by convergence or divergence in the large-scale flow field,realistic mixed layer developments with urban underground are obtained.