A bulk model of the well-mixed boundary layer

A bulk boundary-layer model is developed to predict surface fluxes and conditions in the well-mixed layer between the surface and the lower troposphere. The model includes the effects of all the dominant processes, including advection, in a dry boundary layer. The numerical model is compared with theoretical predictions for the growth of an internal boundary layer, and it is used to simulate the generation of a sea breeze by the diurnal cycle of radiative heating.     

Scaling the atmospheric boundary layer

We review scaling regimes of the idealized Atmospheric Boundary Layer. The main emphasis is given on recent findings for stable conditions. We present diagrams in which the scaling regimes are illustrated as a function of the major boundary-layer parameters. A discussion is given on the different properties of the scaling regimes in unstable and stable conditions.     

Steady-state characteristics of inversions capping a well-mixed planetary boundary layer

The type of inversion discussed in this paper is essentially defined by subsidence, mixing due to thermally generated turbulent energy and a radiative flux difference at the inversion. A concept similar to that of Lilly (1968) is applied, assuming a well-mixed layer below the inversion and including advective and radiative processes.The characteristics of the inversion and of the whole PBL (e.g., height of inversion, height of cloud base, strength of inversion, flux-profiles) are investigated for their dependence on external parameters such as horizontal wind field divergence, advection, surface temperature excess, wind speed and surface temperature. This is done for steady-state conditions and gives considerable insight into the processes maintaining the type of inversion under consideration.A second goal is to present typical inversion structures, which can be found in certain climatic regions. The profiles of the state parameters and the energy-fluxes for the Trade-Wind region, the cold water area off the west-coast of California, the Norwegian Sea and the Arctic Ocean differ considerably.     

On similarity in the atmospheric boundary layer

A similarity theory for the atmospheric boundary layer is presented. The Monin-Obukhov similarity theory for the surface layer is a particular case of this new theory, for the case of z 0. Universal functions which are in agreement with empirical data are obtained for the stable and convective regimes.On leave from Institute of Environmental Engineering, Warsaw Technical University, 00653 Warsaw, Poland. Present address, Department of Geological and Geophysical Sciences, University of Wisconsin, Milwaukee, WI 53201 U.S.A.     

大气边界层研究进展

基于2013—2015年6—8月“第三次青藏高原大气科学试验（TIPEX-Ⅲ）”和常规气象业务探空观测资料、欧洲中期天气预报中心（ECMWF）第5代再分析（ERA-5）数据以及“国际卫星云气候计划（ISCCP）”云量资料,采用统计分析和物理量诊断分析方法,研究了夏季青藏高原（简称高原）大气对流边界层高度东西差异对高原地区天气尺度环流的影响。结果表明：高原对流边界层高度东西差异表现出明显的日变化,且这种差异呈现西高东低的分布特征,主要由西部对流边界层高度明显增大所致。当中午对流边界层高度东西向差异增大时,午后地面虚位温6 h变差呈西部高、东部低的特征,且西部变化更明显,高原西部对流边界层内温度升高,东部略降低,并伴随着高原西部对流边界层内气压降低、高层升高且低压系统较浅薄,而东部低层气压升高;高原低层东高西低的气压场特征产生了异常东西向气压梯度,引起高原中部低层出现偏南风异常,伴随着西部的低层异常辐合和高层异常辐散;同时,浅薄的低压有助于当地低云发展。     

Current problems in the stratocumulus-topped atmospheric boundary layer

Extended sheets of stratocumulus (Sc) in the upper part of the atmospheric boundary layer (ABL) often occur under appropriate meteorological conditions. These cloud decks are important both in climate studies and in weather forecasting. We review the current knowledge of the turbulent structure of the ABL capped by a cloud deck, in the light of recent observations and model studies. The most important physical processes determining this structure are longwave radiative cooling at cloud top, shortwave radiative wanning by absorption in the cloud, surface buoyancy flux, and wind shear in the ABL. As a result, turbulence can cause entrainment against the buoyancy jump at cloud top. In cases where only longwave radiative fluxes and surface buoyancy fluxes are important, the turbulent structure is relatively well understood. When shortwave radiative fluxes and/or wind shear are also important, the resulting turbulent structure may change considerably. A decoupling of the cloud from the sub-cloud layer or of the top of the cloud from the rest of the ABL is then regularly observed. In no cases are the details of the entrainment at cloud top understood well enough to derive a relatively simple formulation that is consistent with observations. Cloud-top entrainment instability may lead to the break-up of a cloud deck (but also to cloud deepening). The role of mesoscale circulations in determining fractional cloudiness is not yet well understood.     

Parametric relations for the atmospheric boundary layer

Some parametric relations for the atmospheric planetary boundary layer (PBL) are suggested for possible use in the various atmospheric circulation and air quality models, as well as in other applications. These are for parameterizing the mean wind and temperature profiles, the vertical fluxes of momentum, heat and moisture, the variances of velocity fluctuations and length and time scales in the PBL. The parametric relations for the PBL height, the vertical velocity at the top of the PBL and the total energy dissipation in the PBL are also discussed. Experimental and/or theoretical bases for the various parametric relation are given. Some of the suggested parameterizations should be considered as tentative, until they are properly validated.     

Scale effects in wind tunnel modeling of an urban atmospheric boundary layer

Precise urban atmospheric boundary layer (ABL) wind tunnel simulations are essential for a wide variety of atmospheric studies in built-up environments including wind loading of structures and air pollutant dispersion. One of key issues in addressing these problems is a proper choice of simulation length scale. In this study, an urban ABL was reproduced in a boundary layer wind tunnel at different scales to study possible scale effects. Two full-depth simulations and one part-depth simulation were carried out using castellated barrier wall, vortex generators, and a fetch of roughness elements. Redesigned “Counihan” vortex generators were employed in the part-depth ABL simulation. A hot-wire anemometry system was used to measure mean velocity and velocity fluctuations. Experimental results are presented as mean velocity, turbulence intensity, Reynolds stress, integral length scale of turbulence, and power spectral density of velocity fluctuations. Results suggest that variations in length-scale factor do not influence the generated ABL models when using similarity criteria applied in this study. Part-depth ABL simulation compares well with two full-depth ABL simulations indicating the truncated vortex generators developed for this study can be successfully employed in urban ABL part-depth simulations.     

Coherent structures in the very stable atmospheric boundary layer

This study examines the structure of horizontal modes (meandering, vortical modes or fossil turbulence) in a layer of intermittent turbulence occurring at the top of a strongly stratified nocturnal inversion layer as observed by fast response aircraft data. The spatial variation of the coefficients of the principal components identify regular coherent structures with mainly horizontal motions. Conditional sampling is formulated in terms of this spatial variation. The quasi-horizontal motions are characterized by relatively sharp edges (transition zones) where horizontal convergence or divergence, small-scale turbulence and vertical fluxes seem to be concentrated. Zones of horizontal divergence appear to be associated with ejection of cold air from the underlying surface inversion while the convergent zones might be due to random collisions between horizontal modes.     

The velocity spectra in the stable atmospheric boundary layer

A model for the logarithmic spectra of velocity in the stable boundary layer is developed using the concept of local scaling. The resulting expressions for peak wavelength are in agreement with empirical data from Minnesota 1973.Partially financed by CAPES and FINEP.On leave from Faculdade de Engenharia de Joinville, SC, Brasil.     

On eddy convection velocity in the atmospheric boundary layer

Lumley's model is extended to predict the effect of convection velocity fluctuations on eddy convection velocity for the high-frequency region of the longitudinal, transverse and scalar phase spectra in the atmospheric boundary layer. The resulting model predicts that the eddy convection velocity will be higher than the mean wind speed. The increase over the mean wind speed is largest for the longitudinal spectrum.     

A TKE-dissipation model for the atmospheric boundary layer

The dissipation, , of turbulent kinetic energy (TKE) is a key parameter in atmospheric boundary-layer (ABL) models. Besides being a sink for momentum, it is often used together with the TKE to define an internal turbulence time scale for closure relations. A prognostic formulation for the dissipation of TKE is formulated, based on isotropic tensor modeling methods. The formulation is coupled to a level 2.5 second-order closure model and evaluated against measurements taken in horizontally homogeneous conditions, as well as against a tailored length-scale formulation. A formulation suitable for convective as well as neutral and stable ABLs is suggested.On leave from Department of Meteorology, Uppsala University, P.O. Box 516, S-751 20 Uppsala, Sweden.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

A parameterization of the stable atmospheric boundary layer

Two formulations of the stable atmospheric boundary layer are proposed for use in weather forecasting or climate models. They feature the log-linear profile near the surface, but are free from the associated critical Richardson number. The diffusion coefficients in the Ekman layer are a natural extension of the surface layer. They are locally determined using wind shear in one case and turbulent kinetic energy in the other. The parameterizations are tested in a one-dimensional model simulating the evolution of the nocturnal boundary layer with and without radiative cooling. Both formulations give very similar results, except near the top of the boundary layer where the transition to the free atmosphere is smoother with the wind shear formulation. A distinctive feature of these schemes is that they retain their simulating skill when resolution is reduced. This is verified for a wide range of situations. In practice, this means that there is no need for a large-scale model to have a level below 50 m or so.     

Large-Eddy Simulation of the stably-stratified atmospheric boundary layer

Large-Eddy Simulation of stable boundary layers (SBLs) has been considered particularly difficult, indeed perhaps impossible with present computational resources. Here we present a new series of successful simulations of SBLs over uniform, flat terrain, using an approach previously successful for neutral and convective conditions, and showing that essentially the same model can handle all three main dry types of atmospheric boundary layer. We consider both technical requirements for successful and accurate SBL simulations and the observed characteristics of the simulated SBL. We discuss the evolution (in some cases to quasi-steady states) and compare with theory and experimental data. Effects of static-stability on the flow are analyzed using one-point and two-point statistics. Results show the development of a shear-driven SBL, with little sign of distinctively wavelike motions. The flow statistics are found to be consistent with local scaling, and that framework is used to compare with other data and theoretical models.     

论大气边界层的局地相似性

本文利用日本气象厅研究所在筑波市213m气象塔1983年观测的湍流资料验证了大气边界层的局地相似性,求出了相似性函数的经验常数.进一步建立了局地湍流统计量同近地面层和边界层顶湍流通量之间的关系.     

Basic entrainment equations for the atmospheric boundary layer

The parameterization of penetrative convection and other cases of turbulent entrainment by the atmospheric boundary layer is reviewed in this paper. The conservation equations for a one-layer model of entrainment are straightforward; all modeling problems arise in the context of the parameterization of various terms in the budget of turbulent kinetic energy. There is no consensus in the literature on the parameterization of shear production and of dissipation. Unfortunately, field experiments are not sufficiently accurate to guide the selection of suitable hypotheses. Carefully designed laboratory experiments are needed to settle the problems that remain.This paper has also been presented as Invited Paper at the Second IAHR Symposium on Stratified Flows, Trondheim, Norway, June 24–27, 1980.Free University, Amsterdam, The Netherlands.     

Experimental investigation of atmospheric boundary layer turbulence

This paper describes how to measure turbulence in the atmospheric boundary layer (ABL) in order to address certain problems in modern atmospheric physics. These problems mainly relate to the Earth's energy budget (including the hydrological cycle) and biogeochemical cycles. Starting from the main characteristic numbers and the basic equations of atmospheric turbulent flow, we show what turbulence parameters are important to measure. Special attention is given to the various methods used to compute the turbulent fluxes. We analyse the range of scales which has to be measured to properly capture the eddies contributing to the turbulent transfers. This range of scales determines what sensors can be used in the atmospheric surface layer and in the ABL. We describe the most widely used instruments and their performances. The principal platforms used to deploy these instruments are examined. Aircraft are described in more details, because they allow a thorough exploration of the ABL. In the last section, some examples of ABL turbulence signals measured in various conditions are presented. These examples illustrate horizontally homogeneous turbulence as well as inhomogeneous signals for which standard analysis techniques cannot be used. We show how some recent techniques, like wavelet transforms, can help to investigate this kind of signal. At the end, we present what would be interesting to do in the near future for the study of ABL turbulence.     

Second-order closure modeling of diffusion in the atmospheric boundary layer

A method for calculating turbulent diffusion in the planetary boundary layer is developed based on Donaldson's second-order closure approach. The resulting partial differential equation for the turbulent mass flux has a hyperbolic character for early times when the plume scale is small compared with the ambient turbulent scale, with a smooth transition to a parabolic, gradient-diffusion-type character when the plume scale is large. Calculations are compared with available estimates from the literature for different values of Rossby number and Richardson number in the ambient atmosphere. Comparison of model predictions with laboratory simulation of diffusion in a free convection, mixed layer is good, with the model able to predict the maximum concentration rising from the ground as observed.This project has been funded in part with Federal funds from the Environmental Protection Agency under contract number EPA 68-02-1310.