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The temperature and wind profiles in the planetary boundary layer (PBL) are investigated. Assuming stationary and homogeneous conditions, the turbulent state in the PBL is uniquely determined by the external Rossby number and the stratification parameters. In this study, a simple two-layer barotropic model is proposed. It consists of a surface (SL) and overlying Ekman-type layer. The system of dynamic and heat transfer equations is closed usingK theory. In the SL, the turbulent exchange coefficient is consistent with the results of similarity theory while in the Ekman layer, it is constant. Analytical solutions for the wind and temperature profiles in the PBL are obtained. The SL and thermal PBL heights are properly chosen functions of the stratification so that from the solutions for wind and temperature, the PBL resistance laws can be easily deduced. The internal PBL characteristics necessary for the calculation (friction velocity, angle between surface and geostrophic winds and internal stratification parameter) are presented in terms of the external parameters. Favorable agreement with experimental data and model results is demonstrated. The simplicity of the model allows it to be incorporated in large-scale weather prediction models as well as in the solution of various other meteorological problems. 相似文献
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While the importance of baroclinicity in determining the structure of the planetary boundary layer (PBL) is well recognized, the actual effect of baroclinicity on the structure is not well understood. Results based on simulations obtained using the turbulent kinetic energy-dissipation rate of turbulent kinetic energy closure model of the turbulent flow in a neutral baroclinic PBL provide additional insight into the role of baroclinicity. The baroclinic PBL is characterized by significant shear production of turbulent kinetic energy throughout the complete boundary-layer depth. The turbulent mixing length is bounded by the presence of a stable temperature inversion layer indicating that the depth of the baroclinic PBL is determined by the inversion height. Significant turbulent shear stresses exist throughout the baroclinic PBL and the air is relatively well-mixed except in the surface layer. 相似文献
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京津冀采暖期大气污染天气特征 总被引：4，自引：0，他引：4
选取2004—2006年京津冀地区采暖期155个区域大气污染日,对当日08:00(或前一日20:00)海平面气压场,结合高空环流特征进行了分析。对影响京津冀区域污染的天气形势划分为5种类型,即高压型、冷锋型、低压型、华北干槽型和均压场型,其中高压型最多,占40.0%。区域污染过程通常对应一次高空环流调整过程,连续性区域污染过程往往由多种天气型影响。地面辐合加上低层逆温和下沉运动阻碍污染物在水平和垂直方向的扩散,在污染源一定的条件下,稳定的大气层结和区域内特殊地形的影响是导致区域污染形成的重要原因。 相似文献
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An efficient, pianetary boundary layer (PBL) model is developed and validated with empirical data for applications in general circulation models (GCMs). The purpose of this PBL model is to establish the turbulent surface fluxes as a function of the principal external PBL parameters in a numerically efficient way. It consists of a surface layer and a mixed layer matched together with the conditions of constant momentum and heat flux at the interface. An algebraic solution to the mean momentum equations describes the mixed-layer velocity profile and thus determines the surface wind vector. The velocity profile is globally valid by incorporating the effect of variable Coriolis force without becoming singular at the equator. Turbulent diffusion depends on atmospheric stability and is modeled in the surface layer by a drag law and with first-order closure in the mixed layer. Radiative cooling in the stably stratified PBL is considered in a simple manner. The coupled system is solved by an iterative method. In order to preserve the computational efficiency of the large-scale model, the PBL model is implemented into the GISS GCM by means of look-up tables with the bulk PBL Richardson number, PBL depth, neutral drag coefficient, and latitude as independent variables.A validation of the PBL model with observed data in the form of Rossby number similarity theory shows that the internal feedback mechanisms are represented correctly. The model, however, underpredicted the sensible heat-flux. A subsequent correction in the turbulence parameterization yields better agreement with the empirical data. The behavior of the principal internal PBL quantities is presented for a range of thermal stabilities and latitudes. 相似文献
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天津市秋季典型环境污染过程个例分析 总被引：2，自引：0，他引：2
选择天津市秋季典型PM10污染过程2010年10月3—12日环境空气质量监测资料和常规气象资料、探空资料及NCEP资料,研究大气环境天气背景场、大气层结稳定度的特征及其对污染过程的影响。结果表明：高低空环流背景场与污染过程密切相关。在污染上升阶段,层结稳定度迅速增加,500 hPa高空处于槽前,地面在华北地形槽中,高低空风速辐合;在污染峰值阶段,层结稳定,逆温层加强,环流场稳定少变,地面风力微弱;在污染下降阶段,层结稳定程度骤降,地面冷锋和高空槽过境,降水出现,高低空偏北风增大。同时,PM10污染过程与多项层结稳定度参数显著相关,与对流凝结高度单相关系数为0.84,因此,高低空环流背景场的配置和层结稳定度变化是PM10污染出现的主要原因。 相似文献
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A puff model is developed in this study, which simultaneously considers the Monte-Carlo technique, the time and space changes of atmospheric parameters, multiple continuity pollutant sources, linear chemical trans-formation and removal of pollutants, and the effect of complex terrain. The continuously observed turbulent statistical quantities, Lagrangian time scales, mesoscale flow field, and mixing layer depth in the PBL in the Dianchi area in China are directly put into the model, and the diurnal variations of air pollution are forecasted, which are dominated by such mesoscale local circulations as mountain and valley breeze, land and lake breeze, and city heat island (Kunming City). The results show that in the case of inputting the same data, they are in good agreement with the experimental data, as well as with the results of the three-dimensional advection-diffusion model (TD-ADM); the diurnal variation of mesoscale local circulation results in the obvious diurnal variation of mesoscale concentration distribution patterns; the Dianchi lake (appr. 300 km2) has a considerable effect on the distribution of air pollution in the area. 相似文献
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1 INTRODUCTION Since the 1930’s, urban air pollution has caused increasing concerns across the world[1]. Various pollution prediction techniques have been put into use in the 1970’s and significant results have been achieved[2]. Air quality prediction has been operational over recent years in many parts of China owing to cooperation between meteorological and environmental protection departments[3 – 9]. The prediction is conducted via either numerical model, potential or stochastic app… 相似文献
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边界层参数化方案在“灰色区域”尺度下的适用性评估 总被引：2，自引：0，他引：2
随着数值预报模式分辨率的提高,当模式网格距与含能湍涡的长度尺度相当时,模式动力过程可解析一部分湍流运动,而剩余的湍流运动仍需参数化,此时便产生了湍流参数化的“灰色区域”问题。对传统的PBL（Planetary Boundary Layer）方案在“灰色区域”下的适用性评估,是改进PBL方案以使其能够适应分辨率变化的前提和基础。本研究基于干对流边界层的大涡模拟试验,比较了WRF（Weather Research and Forecast Model）模式中四种常用的边界层参数化方案[YSU（Yonsei University）、MYJ（Mellor-Yamada-Janjic）、MYNN2.5（Mellor-Yamada-Nakanishi-Niino Level 2.5）、MYNN3）]在“灰色区域”尺度下的表现。研究表明,混合层内总热通量对所使用的参数化方案和水平分辨率均不敏感。不同参数化方案中次网格与网格通量的比例表现出对水平网格距不同的依赖性。局地PBL方案（MYJ、MYNN2.5）在混合层内的平均位温随网格距减小而增大,次网格通量随网格距减小而减小,较参考湍流场对次网格通量有所低估。YSU方案的非局地项几乎不随水平格距改变而变化,对次网格通量的表征并未表现出较强的分辨率依赖性,且过强的非局地次网格输送使混合层内温度层结呈弱稳定,抑制了可分辨湍流输送,不易于激发次级环流。MYNN3方案的非局地次网格通量（负梯度输送项）随网格距减小而减小,使其对次网格通量的表征具有较好的分辨率依赖性。PBL方案在“灰色区域”尺度下的适用性与具体分辨率有关。以分辨率500 m为例,四种PBL方案中不存在一种最佳方案,能对边界层的热力结构和湍流统计特征均有准确的描述。 相似文献
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The formation of longitudinal vortex rolls in the planetary boundary layer (PBL) is investigated by means of perturbation analysis. The method is the same as that used by previous authors who have investigated the instability of a laminar Ekman layer. To study the instability of the turbulent boundary layer of the atmosphere, vertical profiles are needed of the eddy viscosity and of the two components of the basic flow. These profiles have been obtained by a numerical PBL-model; they are universal for zz
0. (However, the stability equations are not completely universal, i.e., independent of the external parameters). For each thermal stratification, expressed by the internal stratification parameter , one has a set of three consistent profiles.The numerical solution of the stability equations gives the critical values and the perturbation growth rates as functions of thermal stratification and of the surface Rossby number Ro0. This is in contrast to the case of a laminar Ekman layer, where the instability depends on a Reynolds number only, which makes atmospheric applications difficult. The most unstable perturbations are found for Ro0 = 1 × 106 approximately, which is in the range of surface Rossby numbers observed in the atmosphere. However, considering vortex rolls oriented in the direction of the surface stress, the instability is found to be universal, i.e., independent of the external parameters combined in the surface Rossby number. With respect to thermal stratification, the results show that the instability of the perturbations increases with increasing static stability. 相似文献
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利用2007--2010年南昌市空气污染监测资料以及气象观测资料,分析了空气质量与天气形势的关系,以及造成南昌市空气污染的主要天气形势特征。结果表明：（1）南昌市空气污染具有明显的季节性变化特征,冬季污染日出现频次最高,其次是春、秋两季,夏季由于雨水的冲刷稀释作用、热对流作用,极少出现空气污染日。（2）影响南昌市空气质量的地面形势主要分为低压类（倒槽、锋前）和高压类（高压底部、高压后部、弱高压）,而高空系统主要为槽后西北气流以及西南气流的影响。（3）当出现空气污染时,地面至1000hPa近地层逆温非常明显,地面风速弱,基本在3m／s以下,且以偏东风出现频次最高。（4）污染物浓度与霾天气密切相关,霾日的空气质量较差。 相似文献
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Ian G. Mckendry 《Boundary-Layer Meteorology》1989,49(1-2):7-22
The air pollution meteorology of a typical sea breeze day is investigated using the Colorado State University Mcsoscale Model. Results are qualitatively compared with observations and reveal a complex wind field characterised by migratory sea breeze convergence zones. Associated with these features, the model predicts enhanced upward vertical velocities and doming of the planetary boundary layer (PBL). The diurnal variation in PBL depth is shown to vary markedly at different locations and is dependent on position in relation to the migratory convergence zones. These complex spatial and temporal variations in the wind and PBL depth have important implications for air quality in Auckland and confirm that simple Gaussian or box trajectory approaches are inappropriate for air quality assessment in such environments. The inclusion in the model of variable surface properties, a dynamic synoptic state and improved PBL parameterisations, as well as coupling with a Lagrangian particle model, are recommended if the model is to be used as a tool for further air quality studies in the Auckland area. 相似文献
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R. A. Brown 《Boundary-Layer Meteorology》1978,14(3):381-396
A two-layer, first-order closure model for the Planetary Boundary Layer (PBL) is developed with the objective of parameterizing the surface stress with respect to the synoptic scale. The model includes stability effects by considering stratification-dependent secondary flow in the outer layer and empirical corrections to the surface layer flow. It shows the compatibility of simple eddy viscosity closure solutions with similarity theory by producing the now well-known Rossby similarity equations. It allows further insight into the Rossby similarity parameters by relating them to a single similarity parameter which is the ratio of the characteristic scales of the PBL and the surface layer.The measured and derived values of the similarity parameters A and B are compared with AIDJEX data and other published values. The variation in these values in stably stratified conditions is predicted and two alternate similarity parameters are calculated, one a constant and the other with a small variation and decreasing influence on the drag coefficient in stable stratification. The result is an empirical resistance law for a geostrophic drag coefficient variation which parameterizes an observed order-of-magnitude change in surface stress with changes in roughness or PBL stratification. This variation is related to similarity parameters characteristic of the region and to measurable changes in the geostrophic departure angle. 相似文献
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The effects of synoptic baroclinicity on the evolution of the stable boundary layer are studied by using a numerical model in which the eddy exchange coefficients are determined from the turbulent kinetic energy and a local turbulent length scale. For model verification, several barotropic simulations are compared with those of higher-order closure models. The model predicts the existence of a value of geostrophic wind shear at which the nocturnal jet reaches its maximum intensity. The mechanism by which ageostrophic flow is generated and the role it plays in the development of the jet are explored. As baroclinicity increases, the directional shear in the wind near the level of the jet increases, thereby allowing the nocturnal inversion to grow to levels well above that of the jet.Journal Paper No. J-11109 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA. Project 2521. 相似文献
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In this paper a 3-D mesoscale PBL dynamic prognostic model for a coastal region with complex terrain was developed to simulate the 3-D flow field under a local sea-land breeze circulation. The output from the PBL model was used as an input to an Eulerian numerical model which can be used to simulate finely the temporal and spatial distributions of an air pollutant (SO2) during a sea-land breeze developing in a coastal region. With respect to its use as a diagnostic model, only a few data would be required to simulate the background winds controlled by a larger scale synoptic system, and then provide initial winds for the PBL model.Having linked the three models and defined the coefficients of turbulent diffusion in a simple form, an integrated 3-D numerical air quality model suitable for the coastal environment was designed. The period of May 29, 1986 was selected for simulating and analysing the distribution of air pollutants over the coastal area of Bohai-sea in Northern China. The results indicated that the calculated concentrations corresponded with the observed ones on the whole. Thus this linked model has been shown to be feasible and useful in practice. 相似文献